The vaccines were administered by a home doctor at Windsor Castle, a royal source said.
To avoid inaccuracies and further speculation, His Majesty, who 94, decided he would disclose that he was vaccinated, the source added. Her husband is 99 years old.
The UK recorded more than 3 million cases of Covid-19 and more than 80,000 deaths, according to data from Johns Hopkins University on Saturday.
The UK reported 1,325 coronavirus-related deaths on Friday – its biggest daily increase in deaths.
In the capital, the Mayor of London declared a “major incident” on Friday, warning that the city’s hospitals were close to being invaded.
“The situation in London is now critical, with the spread of the virus out of control,” Mayor Sadiq Khan said in a statement.
“The number of cases in London has increased rapidly, with more than a third more patients being treated in our hospitals, compared to the peak of the pandemic last April.
“We are declaring a major incident because the threat this virus poses to our city is in crisis,” added Khan. “If we don’t take immediate action now, our [National Health Service] it can be overwhelmed and more people will die. “
CNN’s Zamira Rahim and Amy Woodyatt contributed reports.