Britain's Queen Elizabeth last saw Prime Minister Boris Johnson, who has tested positive for the coronavirus, on March 11 and she remains in good health, Buckingham Palace said Friday.

"The queen last saw the PM on the 11th March and is following all the appropriate advice with regards to her welfare," a palace spokesman said.

The queen, 93, is currently at Windsor Castle, her home to the west of London, with her husband, 98-year-old Prince Philip, and a small staff.

On Wednesday, the monarch was pictured speaking on the telephone as she held her regular weekly audience with Johnson remotely.

Earlier this week, it was revealed that the monarch's son and heir Prince Charles had tested positive for coronavirus. He has mild symptoms and is in good health at his home in Scotland, his office said.

Charles last saw the 93-year-old monarch on the morning of March 12 following an investiture, before the earliest time he is likely to have been infectious, a palace spokesman said.