Britain's Queen Elizabeth II walks, during a visit to the CWGC, the Commonwealth War Graves Commission Air Forces Memorial to attend a service to mark the Centenary of the Royal Australian Air Force in Runnymede, England, Wednesday March 31, 2021. (Steve Reigate/Pool Photo via AP)

Britain's Queen Elizabeth II walks, during a visit to the CWGC, the Commonwealth War Graves Commission Air Forces Memorial to attend a service to mark the Centenary of the Royal Australian Air Force in Runnymede, England, Wednesday March 31, 2021. (Steve Reigate/Pool Photo via AP)

Britain's Queen Elizabeth II smiles, during a visit to the CWGC, the Commonwealth War Graves Commission Air Forces Memorial to attend a service to mark the Centenary of the Royal Australian Air Force in Runnymede, England, Wednesday March 31, 2021. (Steve Reigate/Pool Photo via AP)

Britain's Queen Elizabeth II during a visit to the CWGC, the Commonwealth War Graves Commission Air Forces Memorial to attend a service to mark the Centenary of the Royal Australian Air Force, in Runnymede, England, Wednesday March 31, 2021. (Steve Reigate/Pool Photo via AP)

Britain's Queen Elizabeth II during a visit to the CWGC, the Commonwealth War Graves Commission Air Forces Memorial to attend a service to mark the Centenary of the Royal Australian Air Force, in Runnymede, England, Wednesday March 31, 2021. (Steve Reigate/Pool Photo via AP)

Britain's Queen Elizabeth II gestures during a ceremony to mark the Centenary of the Royal Australian Air Force at the CWGC Air Forces Memorial, Runnymede in Surrey on March 31, 2021. (Photo by Steve REIGATE / POOL / AFP)

Britain's Queen Elizabeth II gestures during a ceremony to mark the Centenary of the Royal Australian Air Force at the CWGC Air Forces Memorial, Runnymede in Surrey on March 31, 2021. (Photo by Steve REIGATE / POOL / AFP)

Britain's Queen Elizabeth II gestures during a ceremony to mark the Centenary of the Royal Australian Air Force at the CWGC Air Forces Memorial, Runnymede in Surrey on March 31, 2021. (Photo by Steve REIGATE / POOL / AFP)

Britain's Queen Elizabeth II gestures on her arrival to mark the Centenary of the Royal Australian Air Force at the CWGC Air Forces Memorial, Runnymede in Surrey on March 31, 2021. (Photo by Steve REIGATE / POOL / AFP)

Britain's Queen Elizabeth II gestures on her arrival to mark the Centenary of the Royal Australian Air Force at the CWGC Air Forces Memorial, Runnymede in Surrey on March 31, 2021. (Photo by Steve REIGATE / POOL / AFP)

Britain's Queen Elizabeth II gestures on her arrival to attend a service to mark the Centenary of the Royal Australian Air Force at the CWGC Air Forces Memorial, Runnymede in Surrey on March 31, 2021. (Photo by Steve REIGATE / POOL / AFP)

Britain's Queen Elizabeth II gestures on her arrival to attend a service to mark the Centenary of the Royal Australian Air Force at the CWGC Air Forces Memorial, Runnymede in Surrey on March 31, 2021. (Photo by Steve REIGATE / POOL / AFP)

Britain's Queen Elizabeth II gestures as Her Majesty's Equerry prepares to lay a wreath on Her behalf during a service to mark the Centenary of the Royal Australian Air Force at the CWGC Air Forces Memorial, Runnymede in Surrey on March 31, 2021. (Photo by Steve REIGATE / POOL / AFP)

Britain's Queen Elizabeth II gestures during a service to mark the Centenary of the Royal Australian Air Force at the CWGC Air Forces Memorial, Runnymede in Surrey on March 31, 2021. (Photo by Steve REIGATE / POOL / AFP)

Britain's Queen Elizabeth II speaks to High Commissioner for Australia, George Brandis (L) during a service to mark the Centenary of the Royal Australian Air Force at the CWGC Air Forces Memorial, Runnymede in Surrey on March 31, 2021. (Photo by Steve REIGATE / POOL / AFP)

Britain's Queen Elizabeth II takes part in a ceremony to mark the Centenary of the Royal Australian Air Force at the CWGC Air Forces Memorial, Runnymede in Surrey on March 31, 2021. (Photo by Steve REIGATE / POOL / AFP)

Britain's Queen Elizabeth II takes part in a ceremony to mark the Centenary of the Royal Australian Air Force at the CWGC Air Forces Memorial, Runnymede in Surrey on March 31, 2021. (Photo by Steve REIGATE / POOL / AFP)

Britain's Queen Elizabeth II takes part in a ceremony to mark the Centenary of the Royal Australian Air Force at the CWGC Air Forces Memorial, Runnymede in Surrey on March 31, 2021. (Photo by Steve REIGATE / POOL / AFP)

Britain's Queen Elizabeth II gestures during a service to mark the Centenary of the Royal Australian Air Force at the CWGC Air Forces Memorial, Runnymede in Surrey on March 31, 2021. (Photo by Steve REIGATE / POOL / AFP)

Britain's Queen Elizabeth II gestures during a service to mark the Centenary of the Royal Australian Air Force at the CWGC Air Forces Memorial, Runnymede in Surrey on March 31, 2021. (Photo by Steve REIGATE / POOL / AFP)

Britain's Queen Elizabeth II gestures as Her Majesty's Equerry prepares to lay a wreath on Her behalf during a service to mark the Centenary of the Royal Australian Air Force at the CWGC Air Forces Memorial, Runnymede in Surrey on March 31, 2021. (Photo by Steve REIGATE / POOL / AFP)

Britain's Queen Elizabeth II looks on during a service to mark the Centenary of the Royal Australian Air Force at the CWGC Air Forces Memorial, Runnymede in Surrey on March 31, 2021. (Photo by Steve REIGATE / POOL / AFP)

Britain's Queen Elizabeth II looks on during a service to mark the Centenary of the Royal Australian Air Force at the CWGC Air Forces Memorial, Runnymede in Surrey on March 31, 2021. (Photo by Steve REIGATE / POOL / AFP)

Britain's Queen Elizabeth II looks on during a service to mark the Centenary of the Royal Australian Air Force at the CWGC Air Forces Memorial, Runnymede in Surrey on March 31, 2021. (Photo by Steve REIGATE / POOL / AFP)

Image Licensed to i-Images Picture Agency. 31/03/2021. Runnymede, United Kingdom. Queen Elizabeth II at a service to mark the centenary of the Royal Australian Air Force at the Commonwealth War Graves Commission Air Forces Memorial in Runnymede, United Kingdom. Picture by i-Images / Pool

Image Licensed to i-Images Picture Agency. 31/03/2021. Runnymede, United Kingdom. Queen Elizabeth II at a service to mark the centenary of the Royal Australian Air Force at the Commonwealth War Graves Commission Air Forces Memorial in Runnymede, United Kingdom. Picture by i-Images / Pool

Image Licensed to i-Images Picture Agency. 31/03/2021. Runnymede, United Kingdom. Queen Elizabeth II at a service to mark the centenary of the Royal Australian Air Force at the Commonwealth War Graves Commission Air Forces Memorial in Runnymede, United Kingdom. Picture by i-Images / Pool

Image Licensed to i-Images Picture Agency. 31/03/2021. Runnymede, United Kingdom. Queen Elizabeth II at a service to mark the centenary of the Royal Australian Air Force at the Commonwealth War Graves Commission Air Forces Memorial in Runnymede, United Kingdom. Picture by i-Images / Pool

Image Licensed to i-Images Picture Agency. 31/03/2021. Runnymede, United Kingdom. Queen Elizabeth II at a service to mark the centenary of the Royal Australian Air Force at the Commonwealth War Graves Commission Air Forces Memorial in Runnymede, United Kingdom. Picture by i-Images / Pool

Image Licensed to i-Images Picture Agency. 31/03/2021. Runnymede, United Kingdom. Queen Elizabeth II at a service to mark the centenary of the Royal Australian Air Force at the Commonwealth War Graves Commission Air Forces Memorial in Runnymede, United Kingdom. Picture by i-Images / Pool

Image Licensed to i-Images Picture Agency. 31/03/2021. Runnymede, United Kingdom. Queen Elizabeth II at a service to mark the centenary of the Royal Australian Air Force at the Commonwealth War Graves Commission Air Forces Memorial in Runnymede, United Kingdom. Picture by i-Images / Pool

Image Licensed to i-Images Picture Agency. 31/03/2021. Runnymede, United Kingdom. Queen Elizabeth II at a service to mark the centenary of the Royal Australian Air Force at the Commonwealth War Graves Commission Air Forces Memorial in Runnymede, United Kingdom. Picture by i-Images / Pool

Image Licensed to i-Images Picture Agency. 31/03/2021. Runnymede, United Kingdom. Queen Elizabeth II at a service to mark the centenary of the Royal Australian Air Force at the Commonwealth War Graves Commission Air Forces Memorial in Runnymede, United Kingdom. Picture by i-Images / Pool