First lady Jill Biden tests positive for COVID-19

First lady Jill Biden has tested positive for COVID-19 while on vacation with the president and their family, according to her office.

Jill Biden tested negative on Monday during her routine testing, and then developed "cold-like symptoms" Monday night, according to her communications director, Elizabeth Alexander.

"She tested negative again on a rapid antigen test, but a PCR test came back positive," Alexander said in a statement Tuesday morning.

When President Joe Biden returned from vacation and arrived at Joint Base Andrews Tuesday afternoon, he told reporters that his wife is "feeling well."

"She has to quarantine, then she'll be home," he added.

Jill Biden, who is double vaccinated and twice boosted, has "mild symptoms," Alexander said.

Jill Biden been prescribed the antiviral treatment Paxlovid, which President Biden also took after testing positive last month.

President Biden first tested positive for COVID-19 on July 21, experiencing symptoms including a cough and sore throat. He isolated and completed a five-day course of Paxlovid before testing negative. He then experienced a rebound infection, testing positive again. On Aug. 6, the president's doctor said Biden had received a negative test and was clear to break his isolation.

President Biden, who had been vacationing with his wife and family in Kiawah Island, South Carolina, is considered a close contact and will mask while indoors for the next 10 days and when he's in close contact to others, according to the White House.

The president tested negative for COVID-19 Tuesday morning, and his testing will be increased in light of the first lady testing positive.

Jill Biden will isolate for at least five days. She'll remain "at a private residence in South Carolina and will return home after she receives two consecutive negative COVID tests," Alexander said.

Her close contacts have been notified, Alexander added.

ABC News' Molly Nagle and Sarah Kolinovsky contributed to this report.