Fears are mounting for the Queen's health as she met with Prince Charles just two days before he tested positive for Covid-19.
But Buckingham Palace is refusing to confirm whether she also has the virus, reports the Daily Mail.
The Queen, 95, is not showing any symptoms so far and palace sources say she is under observation.
It's understood that she has been triple-vaccinated and will not need to self-isolate unless she tests positive. She will be advised to take rapid lateral flow tests over the next seven days.
The Queen received her first dose of the vaccine in January 2021 and her second in March, while sources say she got her booster dose last October.
It's the second time Prince Charles, 73, has tested positive for coronavirus after first coming down with the disease in March 2020. He will now self-isolate for 10 days.
Aides say the prince had a positive result from a routine test, suggesting he had not been experiencing strong symptoms, but they declined to give further details on his condition.
Both he and Camilla, Duchess of Cornwall, have been getting tested regularly ahead of official engagements. Camilla, 74, had a negative test on Thursday. Under the UK's current Covid restrictions, Camilla does not need to self-isolate as she is fully vaccinated.
In the past, all those who had come into contact with Charles would have had to self-isolate, but it is no longer a requirement.
It comes just a day after the British Prime Minister Boris Johnson announced that all virus restrictions in the UK would be axed by the end of the month "provided the current encouraging trends in the data continue".
As well as meeting with his mother this week at Windsor, Charles also handed out OBEs to chefs Fergus Henderson, who has Parkinson's disease, and his wife Margot as well as an MBE to Dr Nisreen Alwan, a campaigner for awareness around long Covid.
On February 9, he visited the National Gallery and attended a dinner at the British Museum with Camilla and politicians Rishi Sunak and Priti Patel.