The Duchess of Cornwall has tested positive for Covid, Clarence House has confirmed.
Camilla, who is triple vaccinated, is self-isolating after catching the virus for the first time, several days after carrying out a series of public engagements.
The Prince of Wales tested positive for the second time on Thursday, with Buckingham Palace declining to confirm whether the Queen, who saw him last week, had caught it too.
A Clarence House spokesman said: "Her Royal Highness the Duchess of Cornwall has tested positive for Covid-19 and is self-isolating. We continue to follow government guidelines."
Clarence House declined to elaborate on whether the Duchess had mild symptoms of the illness, or whether she had spent Valentine's Day with her husband now that they are both isolating.
The couple are last known to have spent the evening together on Wednesday, when they attended a British Asian Trust event. The Prince tested positive in a routine test for Covid the next morning, and was said to have suffered no symptoms at that point.
The Duchess, 74, said that "luckily" she was negative later the same day, adding of her testing regime during a visit to Thames Valley Partnership in Buckinghamshire: "I've taken it so many times".
She continued with her programme of public engagements at the end of last week, visiting charities after the negative test.
Those who attended the events have now been notified of her test result as a precautionary measure. The charities have begun the process of contacting the scores of people who were in close contact with Camilla, who wore a mask for only parts of the engagements when required.
The news will increase concern over the health of the Queen, who saw the Prince of Wales in person at Windsor Castle on Tuesday, two days before his positive Covid test.
Buckingham Palace has declined to confirm Her Majesty's testing status. She is due to be working at Windsor Castle this week on virtual engagements via video link on Tuesday.
According to government guidelines, when the Prince tested positive the Duchess was not required to self-isolate because she was fully vaccinated. She has followed recommendations to begin taking lateral flow tests every day for seven days.
When Prince Charles first caught Covid at the start of the first lockdown in March 2020, Camilla escaped it but self-isolated as a precaution.
The Duke of Cambridge is now known to have also contracted Covid in April 2020, but did not announce it through aides for fear of worrying the public.