The Prince of Wales, who is self-isolating after testing positive for Covid-19, met the Queen two days ago in Windsor, a royal source says.
They say the monarch is not showing any symptoms of coronavirus.
Prince Charles tested positive on Thursday morning - it is the second time he has contracted the virus.
The previous evening, he and the Duchess of Cornwall met Chancellor Rishi Sunak and others at a reception in the British Museum.
Camilla has tested negative for coronavirus, Clarence House said.
Buckingham Palace has not confirmed whether the Queen has tested positive or negative, citing medical privacy.
Earlier this week, Charles held an investiture at Windsor Castle, where the Queen, 95, is currently in residence.
The 73-year-old heir to the throne last caught the virus in March 2020, when he reported only mild symptoms.
Clarence House confirmed he was now triple vaccinated, but would not give any detail on whether he was experiencing coronavirus symptoms this time.
Photo PA Media Caption: Prince Charles caught coronavirus in March 2020 but only had mild symptoms