Members of The King's Troop Royal Horse Artillery fire a gun salute to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Alastair Grant/Pool via REUTERS

Members of The King's Troop Royal Horse Artillery stand by as a gun salute is fired to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Alastair Grant/Pool via REUTERS

A member of The King's Troop Royal Horse Artillery prepares empty shells to be used during a gun salute to commemorate the death of Britain's Prince Philip, Duke of Edinburgh, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Alastair Grant/Pool via REUTERS

A member of The King's Troop Royal Horse Artillery prepares empty shells to be used during a gun salute to commemorate the death of Britain's Prince Philip, Duke of Edinburgh, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Alastair Grant/Pool via REUTERS

A girl holds a letter in front of flowers at Hillsborough Castle after Britain's Prince Philip, husband of Queen Elizabeth, died at the age of 99, in Hillsborough, Northern Ireland, April 10, 2021. REUTERS/Jason Cairnduff

A man brings flowers to Hillsborough Castle after Britain's Prince Philip, husband of Queen Elizabeth, died at the age of 99, in Hillsborough, Northern Ireland, April 10, 2021. REUTERS/Jason Cairnduff

People bring flowers to Buckingham Palace after Britain's Prince Philip, husband of Queen Elizabeth, died at the age of 99, in London, Britain, April 10, 2021. REUTERS/Henry Nicholls

Children holding flowers stand outside Buckingham Palace after Britain's Prince Philip, husband of Queen Elizabeth, died at the age of 99, in London, Britain, April 10, 2021. REUTERS/Henry Nicholls

Children holding flowers stand outside Buckingham Palace after Britain's Prince Philip, husband of Queen Elizabeth, died at the age of 99, in London, Britain, April 10, 2021. REUTERS/Henry Nicholls

A man bows in front of flowers placed at Hillsborough Castle after Britain's Prince Philip, husband of Queen Elizabeth, died at the age of 99, in Hillsborough, Northern Ireland, April 10, 2021. REUTERS/Jason Cairnduff

Members of The King's Troop Royal Horse Artillery attend a gun salute to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Daniel Leal-Olivas/Pool via REUTERS

Members of The King's Troop Royal Horse Artillery fire a gun salute to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Alastair Grant/Pool via REUTERS

General practitioner Kerem Erekul fills in the vaccination certificate after a man received a dose of the AstraZeneca coronavirus disease (COVID-19) vaccine in a doctor's practice in Berlin, Germany, April 10, 2021. REUTERS/Fabrizio Bensch

Rugby Union - European Challenge Cup Quarter Final - Leicester Tigers v Newcastle Falcons - Welford Road Stadium, Leicester, Britain - April 10, 2021 Newcastle Falcons' George Wacokecoke scores their first try Action Images via Reuters/John Sibley

Members of The King's Troop Royal Horse Artillery fire a gun salute to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Alastair Grant/Pool via REUTERS

Members of The King's Troop Royal Horse Artillery fire a gun salute to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Alastair Grant/Pool via REUTERS

Members of The King's Troop Royal Horse Artillery fire a gun salute to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Alastair Grant/Pool via REUTERS

Members of The King's Troop Royal Horse Artillery fire a gun salute to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Hollie Adams/Pool via REUTERS

Members of The King's Troop Royal Horse Artillery prepare to fire a gun salute to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Hollie Adams/Pool via REUTERS

Vials of the AstraZeneca and Pfizer-BioNTech Comirnaty coronavirus disease (COVID-19) vaccines are pictured in a General practitioners practice in Berlin, Germany, April 10, 2021. REUTERS/Fabrizio Bensch

Members of The King's Troop Royal Horse Artillery prepare to fire a gun salute to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Hollie Adams/Pool via REUTERS

Members of The King's Troop Royal Horse Artillery prepare to fire a gun salute to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Hollie Adams/Pool via REUTERS

A man receives a dose of the Pfizer-BioNTech Comirnaty coronavirus disease (COVID-19) vaccine by general practitioner Peter Karsten in a doctor's practice in Berlin, Germany, April 10, 2021. REUTERS/Fabrizio Bensch

A man receives at his home a dose of the AstraZeneca coronavirus disease (COVID-19) vaccine by general practitioner Peter Karsten in Berlin, Germany, April 10, 2021. REUTERS/Fabrizio Bensch

Rugby Union - European Challenge Cup Quarter Final - Leicester Tigers v Newcastle Falcons - Welford Road Stadium, Leicester, Britain - April 10, 2021 Newcastle Falcons' Tom Penny in action with Leicester Tigers' Kini Murimurivalu Action Images via Reuters/John Sibley

Children holding flowers stand outside Buckingham Palace after Britain's Prince Philip, husband of Queen Elizabeth, died at the age of 99, in London, Britain, April 10, 2021. REUTERS/Henry Nicholls

Rugby Union - European Challenge Cup Quarter Final - Leicester Tigers v Newcastle Falcons - Welford Road Stadium, Leicester, Britain - April 10, 2021 Leicester Tigers' Richard Wigglesworth in action with Newcastle Falcons' Micky Young Action Images via Reuters/John Sibley

Members of The King's Troop Royal Horse Artillery fire a gun salute to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Alastair Grant/Pool via REUTERS

Members of The King's Troop Royal Horse Artillery fire a gun salute to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Alastair Grant/Pool via REUTERS

Members of The King's Troop Royal Horse Artillery fire a gun salute to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Alastair Grant/Pool via REUTERS

A woman takes a picture of photos depicting Britain's Prince Philip, husband of Queen Elizabeth, who died at the age of 99, outside a pub in Windsor, near London, Britain, April 10, 2021. REUTERS/Andrew Boyers

Photos depict Britain's Prince Philip, husband of Queen Elizabeth, who died at the age of 99, outside a pub in Windsor, near London, Britain, April 10, 2021. REUTERS/Andrew Boyers

A demonstrator is dressed up as a coronavirus to protest against COVID-19 measures in Vienna, Austria, April 10, 2021. REUTERS/Lisi Niesner

A member of the 105th Regiment Royal Artillery stands guard during a gun salute to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at Edinburgh Castle, Britain April 10, 2021. Andrew Milligan/Pool via REUTERS

A demonstrator is dressed up as a coronavirus to protest against COVID-19 measures in Vienna, Austria, April 10, 2021. REUTERS/Lisi Niesner

A demonstrator is dressed up as a coronavirus to protest against COVID-19 measures in Vienna, Austria, April 10, 2021. REUTERS/Lisi Niesner

Horse Racing - Grand National Festival - Aintree Racecourse, Liverpool, Britain - April 10, 2021 General view of the race course Pool via REUTERS/Peter Powell

A man receives a dose of the AstraZeneca coronavirus disease (COVID-19) vaccine by general practitioner Kerem Erekul in a doctors practice in Berlin, Germany, April 10, 2021. REUTERS/Fabrizio Bensch

Members of the 105th Regiment Royal Artillery stand guard during a gun salute to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at Edinburgh Castle, Britain April 10, 2021. Andrew Milligan/Pool via REUTERS

A man receives a dose of the AstraZeneca coronavirus disease (COVID-19) vaccine by general practitioner Kerem Erekul in a doctors practice in Berlin, Germany, April 10, 2021. REUTERS/Fabrizio Bensch

Horse Racing - Grand National Festival - Aintree Racecourse, Liverpool, Britain - April 10, 2021 Ground staff prepare the race track ahead of the racing Pool via REUTERS/Peter Powell

General practitioner Julia Erekul-Tschirner displays empty vials of the Pfizer-BioNTech Comirnaty and AstraZeneca coronavirus disease (COVID-19) vaccines in her doctor's practice in Berlin, Germany, April 10, 2021. REUTERS/Fabrizio Bensch

Gun salute is fired by The King's Troop Royal Horse Artillery to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Hollie Adams/Pool via REUTERS

Gun salute is fired by The King's Troop Royal Horse Artillery to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Hollie Adams/Pool via REUTERS

Gun salute is fired by The King's Troop Royal Horse Artillery to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Hollie Adams/Pool via REUTERS

Gun salute is fired by The King's Troop Royal Horse Artillery to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Hollie Adams/Pool via REUTERS

Gun salute is fired by The King's Troop Royal Horse Artillery to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Daniel Leal-Olivas/Pool via REUTERS

A man lays flowers in front of flowers placed at Hillsborough Castle after Britain's Prince Philip, husband of Queen Elizabeth, died at the age of 99, in Hillsborough, Northern Ireland, April 10, 2021. REUTERS/Jason Cairnduff

Attendees gather as military vehicles from China displayed during the Iraq Defense Exhibition (IQDEX) at the Baghdad International Fair, Iraq, April 10, 2021. REUTERS/Thaier Al-Sudani

Rugby Union - European Challenge Cup Quarter Final - Leicester Tigers v Newcastle Falcons - Welford Road Stadium, Leicester, Britain - April 10, 2021 General view of players during a two minute silence after Britain's Prince Philip, husband of Queen Elizabeth, died at the age of 99 Action Images via Reuters/John Sibley

Attendees gather as military vehicles from China displayed during the Iraq Defense Exhibition (IQDEX) at the Baghdad International Fair, Iraq, April 10, 2021. REUTERS/Thaier Al-Sudani

Photos depict Britain's Prince Philip, husband of Queen Elizabeth, who died at the age of 99, outside a pub in Windsor, near London, Britain, April 10, 2021. REUTERS/Andrew Boyers

A photo depicts Britain's Prince Philip, husband of Queen Elizabeth, who died at the age of 99, outside a pub in Windsor, near London, Britain, April 10, 2021. REUTERS/Andrew Boyers

Vials of the Pfizer-BioNTech Comirnaty coronavirus disease (COVID-19) vaccine are pictured in a General practitioners practice in Berlin, Germany, April 10, 2021. REUTERS/Fabrizio Bensch

Models of weapons from Pakistan are displayed during the Iraq Defense Exhibition (IQDEX) at the Baghdad International Fair, Iraq, April 10, 2021. REUTERS/Thaier Al-Sudani

Gun salute is fired by The King's Troop Royal Horse Artillery to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Daniel Leal-Olivas/Pool via REUTERS

Gun salute is fired by The King's Troop Royal Horse Artillery to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Daniel Leal-Olivas/Pool via REUTERS

A girl walks in front of flowers placed at Hillsborough Castle after Britain's Prince Philip, husband of Queen Elizabeth, died at the age of 99, in Hillsborough, Northern Ireland, April 10, 2021. REUTERS/Jason Cairnduff

Models of weapons from Turkey are displayed during the Iraq Defense Exhibition (IQDEX) at the Baghdad International Fair, Iraq, April 10, 2021. REUTERS/Thaier Al-Sudani

Gun salute is fired by The King's Troop Royal Horse Artillery to mark the death of Britain's Prince Philip, husband of Queen Elizabeth, at the Parade Ground, Woolwich Barracks in central London, Britain April 10, 2021. Daniel Leal-Olivas/Pool via REUTERS