Britain's Boris Johnson and Carrie Symonds are having a baby. And engaged.

The unwed couple - the first to occupy 10 Downing Street in such a fashion - also revealed they had become engaged, very quietly, at the end of last year.

The baby is due in early summer, and it was not immediately known whether the couple will wed before or after the birth.

Symonds, 31, is one of youngest partners of a prime minister in centuries, the BBC reported, and Johnson will be the first prime minister to marry while in office in nearly 200 years. At 55, the mop-headed prime minister is almost a quarter-century older than his fiancee.

Though he won't be the the first serving prime minister to have a baby while in office, it is not common. David Cameron and his wife Samantha had a daughter in 2010, shortly after Cameron became prime minister. Before that, Tony Blair and his wife Cherie had a son in 2000, three years into Blair's decade in office. Prior to Blair, no serving prime minister became a parent for more than 150 years.

Symonds wrote a message on her Instagram account, admitting, "I wouldn't normally post this kind of thing on here but I wanted my friends to find out from me."

She said, "Many of you already know, but for my friends that still don't, we got engaged at the end of last year . . . and we've got a baby hatching early summer. Feel incredibly blessed."

This will be Johnson's third marriage. Earlier this month, Johnson reached a divorce settlement with Marina Wheeler, a British lawyer he married in 1993. The couple, who were childhood friends, have four children. They separated in 2018.

Johnson met his first wife, Allegra Mostyn-Owen, when they were both students at Oxford University. They married in 1987 when they were 23-years-old. Twelve days after their divorce in 1993, Johnson married Wheeler, who was visibly pregnant with their first child.

That Johnson and Symonds were an unmarried couple living together at the prime minister's official residence at 10 Downing Street did not seem to faze the British public. Pollsters found most Brits shrugged.

Johnson led his Conservative Party to a landslide victory over the opposition Labour Party in December. Before they became an item, Symonds was a top communications adviser for the Conservative Party. She is now a campaigner to protect the oceans and often posts photos of the couple's scruffy rescue dog Dilyn.

The Guardian ran a scoop back in June about an argument - what Brits called a "row" - that brought police to the apartment Johnson shared with Symonds back then.

A neighbor taped the argument and played it for the newspaper, including shouts heard through the wall from Symonds of "Get off me" and "You just don't care for anything, because you're spoilt." The Guardian reported that wine was drunk and spilled.

Johnson, too, has weathered a string of unflattering revelations over his relations with women. In June, a Sunday Times columnist claimed that Johnson groped her thigh - "high up" - at a boozy lunch in 1999 when he was editor of the Spectator magazine.

"Untrue," said 10 Downing Street.

More recently he also accused of abusing his position as mayor of London to grant favorable treatment to a friend, U.S. entrepreneur Jennifer Arcuri.

Arcuri, who received thousands of pounds from a government agency that Johnson oversaw, told friends she and Johnson were having an affair, according to British news reports.

In November, less than a month before the general election, Arcuri did the round of interviews on British TV and she once had a "very special relationship" with Johnson.

She complained that the prime minister was no longer taking her calls, but had fed her "to the wolves" while ghosting her like "some fleeting one-night stand."

Johnson's colorful personal life has got him into trouble before. In 2004, he was fired from his junior minister role in the Conservative Party after he lied about having an affair with the journalist Petronella Wyatt.

When Johnson as initially asked about the affair, he called the allegations ""an inverted pyramid of piffle."

Johnson doesn't like to talk about his private life. When he was asked late last year on LBC radio if he had four or five children, he replied, "I love my children very much but they are not standing at this election. I'm not therefore going to comment on them."

Johnson is believed to have a daughter from an extramarital affair with art consultant Helen Macintyre.