Queen Elizabeth, 95, has tested positive for COVID and is experiencing mild symptoms, Buckingham Palace said on Sunday.
"The queen has today tested positive for COVID," the Palace said. "Her Majesty is experiencing mild cold like symptoms but expects to continue light duties at Windsor over the coming week.
"She will continue to receive medical attention and will follow all appropriate guidelines."
Charles, 73, the heir to the throne, earlier this month pulled out of an event after contracting coronavirus for a second time. A palace source said he had met the queen just days before.
The health of the queen, the world's oldest and longest-reigning monarch, has been in the spotlight since she spent a night in hospital last October for an unspecified ailment and then was advised by her doctors to rest.
Elizabeth on Wednesday quipped to members of the royal household that she could not move much as she carried out her first in-person engagement since Charles tested positive.
The US House of Representatives rejected an effort on Thursday to stop President Donald Trump's air war on Iran and require that any hostilities against Iran be authorized by Congress, backing the Republican president's military campaign.
Foreign ministers from the Gulf Cooperation Council (GCC) and the European Union have strongly condemned the Iranian attacks targeting GCC states, calling them a direct threat to regional and global security.
US President Donald Trump claimed the right to join Iran in deciding its next leader as the war escalated, with US and Israeli jets hitting areas across the country and Gulf cities coming under renewed attack.
British Prime Minister Keir Starmer said on Thursday that four additional Typhoon fighter jets would be sent to Qatar amid the ongoing regional developments, insisting that the UK has the right plan for defence.