The palace just released a statement revealing the news, despite the 39-year-old Duchess of Cambridge being exposed nearly four days ago.
According to a spokesperson for Kensington Palace, Middleton came into contact with someone who tested positive for the virus on Friday -- just one day after Harry and William put their royal feud aside to unveil their mom Princess Diana's statue.
Middleton joined the feuding brothers on the day of the event.
"Her Royal Highness is not experiencing any symptoms, but is following all relevant government guidelines and is self-isolating at home," the palace spokesperson said in a statement on Monday.
Despite getting both vaccinations and experiencing no symptoms, Middleton will take a break from royal duties while she quarantines for the required 10-day period.
She will not be in attendance for Monday's engagement, revealed the palace.
As Radar reported, Harry and William reunited for the first time in months last week.
The brothers were all smiles in front of cameras for the event honoring what would have been their mom's 60th birthday, but Radar learned Harry refused to cooperate behind the scenes.
“No one in the world plans an event better than The Royal Family. There is no detail too small which is why Harry’s lack of communication is making everyone very nervous,” sources told us ahead of the event.
“This is just not the way they do things. Harry won’t show them his speech and is refusing to take part in meetings or dress rehearsals. He seems to want to just wing it. To just turn up and see what happens. They don’t even know what he is planning to wear," one insider revealed.
Harry isolated for five days after arriving in the U.K. He skipped out, heading back to California almost immediately after.
Following Diana's statue unveiling, Middleton attended several events, including sitting courtside at Wimbledon.