Prince Charles's wife Camilla, the Duchess of Cornwall, has tested positive for COVID-19.
Clarence House said the 74-year-old was self-isolating after the result.
"Her Royal Highness The Duchess of Cornwall has tested positive for COVID-19 and is self-isolating," Clarence House said in a statement.
"We continue to follow government guidelines."
The announcement from Clarence House comes four days after it announced Prince Charles's positive result – the second time he has tested positive.
There was no update on his condition on Monday, but both he and Camilla have been fully vaccinated including a booster shot.
Camilla had carried out several engagements on Thursday after her husband's positive test as she had returned a negative test, which is allowed under government guidelines.
There were concerns for the Queen's health after a royal source revealed Charles had met his mother on Tuesday of last week – two days before his positive COVID-19 result.
The source said the Queen, who is also believed to have had three vaccinations – was not experiencing any symptoms and was being monitored.
Charles previously tested positive for the virus in March 2020, when he said he had been "lucky" to have suffered only mild symptoms.
His son Prince William also contracted COVID shortly after his father in 2020.
During her engagements on Thursday, Camilla said she was "very, very honoured" and "very touched" by the Queen publicly stating her desire that she become Queen Consort when Charles becomes King.
