Boris Johnson to marry pregnant partner Carrie Symonds with baby due early summer

Mr Johnson and his second wife, Marina Wheeler, are in the process of a divorce. (Image: AFP/Getty Images)

Boris Johnson’s girlfriend Carrie Symonds is about five months pregnant with the couple’s first child - dubbed a 'Brexit baby' - and they are engaged to be married.

After telling family and close friends, Ms Symonds put rumours to rest and announced the news on her private Instagram profile, writing: "We got engaged at the end of last year... and we've got a baby hatching early summer."

The boy or girl will be the sixth child with three different women for the Prime Minister, who is still married to his second wife and proposed to his soon-to-be third wife around Christmas and New Year's.

He will become the first British prime minister to marry in office for 250 years and the first to have a child in office since David and Samantha Cameron welcomed their daughter Florence.

An early summer birth would suggest the new arrival was conceived during the Autumn, around the time that the October 31 Brexit deadline was extended.

Mr Johnson, 55, had four children - all adults now - with his estranged spouse Marina Wheeler and a love child who was conceived during an affair with property developer Helen Macintyre.

Asked as recently as December’s general election campaign, Mr Johnson has repeatedly refused to reveal how many children he has fathered, but Ms Symonds’ pregnancy has cast a new spotlight on the guarded politician’s family life.

Mr Johnson is believed to be the first prime minister to get divorced and marry in office in modern times. The last PM to do so was Augustus Henry FitzRoy, the 3rd Duke of Grafton, who became prime minister in 1768 and got divorced and remarried the following year.

There had been speculation for weeks that Ms Symonds - the first unmarried partner of a prime minister to reside in 10 Downing Street - was pregnant.

The couple chose to live in the four-bedroom flat at No11 instead of the smaller two-bedroom official residence at No10.

Ms Symonds confirmed the pregnancy and engagement news on Instagram, posting a photo showing Mr Johnson kissing her cheek while she is beaming.

It was unknown if they have set a wedding date. Bookies are already taking bets on baby names, with Charlotte, James, Stanley and Winston among the early favourites.

Ms Symonds wrote on Saturday: "I wouldn't normally post this kind of thing on here but I wanted my friends to find out from me...

"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.

"Feeling incredibly blessed."

A spokesperson for the couple said: "The Prime Minister and Miss Symonds are very pleased to announce their engagement and that they are expecting a baby in the early summer."

Mum-to-be Ms Symonds, 31, has rarely been seen in public in recent months and has been keeping a low profile since Mr Johnson won last December’s general election.

In mid-February she was pictured leaving Downing Street via a back entrance, and she is said to have spent increasingly more time at Chequers, the Prime Minister’s country house in Buckinghamshire, this winter.

The couple - who recently adopted a Jack Russell-cross puppy called Dilyn - spent New Year’s Eve on the exclusive Caribbean island of Mustique, where they stayed at a VIP villa that cost an estimated £29,500 for ten days.

But they spent much of the time out of the public eye, and it is possible that he popped the question during their five-star getaway.

The pregnancy and engagement announcement came amid speculation that Mr Johnson - who years ago wrote an article describing the children of single mothers as “ill-raised, ignorant, aggressive and illegitimate” - and Ms Symonds would get married soon after his divorce with Ms Wheeler is finalised.

During the December campaign he refused to answer whether he and Ms Symonds were considering having children or tying the knot.

PM's turbulent love life and affairs

The divorce between Mr Johnson, whose love life and extra-marital affairs have been well documented over the years, and Ms Wheeler recently moved a step closer to being approved after the former lovers ended a year-long dispute over money.

The Prime Minister was frequently accused of adultery during their marriage and fathered a love child born to Ms Macintyre in 2009.

Not a lot is know about his youngest child, Stephanie Macintyre, and it's believed that she doesn't have anything to do with her dad or half-siblings.

His first marriage, to Allegra Mostyn-Owen in 1987, collapsed because of his adultery. The pair met while they were students at Oxford. Their marriage was annulled in 1993, and 12 days later he married Ms Wheeler.

Mr Johnson was sacked from the Tory front bench in 2004 for lying about an affair with the journalist Petronella Wyatt, which led to her having an abortion.

The Appeal Court ruled in 2013 that the public had a right to know he had fathered a daughter during an adulterous liaison while Mayor of London in 2009.

Claims that Mr Johnson squeezed the thigh of journalist Charlotte Edwardes, at a private lunch at The Spectator magazine's HQ shortly after he became editor in 1999, overshadowed his first Conservative Party conference as PM.

But in a public display of affection, Mr Johnson kissed Ms Symonds after his speech to party members at the event.

Mr Johnson greeted Cabinet ministers before embracing his girlfriend, kissing her on the cheek and then walking out of the hall holding her hand.

Meanwhile, allegations about Mr Johnson's relationship with American entrepreneur Jennifer Arcuri, and whether she enjoyed preferential treatment while he was London mayor, also dominated the headlines in September.