Boris Johnson and Carrie Symonds have announced they are expecting a baby and are engaged.
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.”
Mr Johnson, 55, and Miss Symonds, 31, made history as the first unmarried couple to officially live together in Downing Street when they moved in last year.
Ms Symonds, a conservationist and former Conservative Party communications chief, made headlines when she was romantically linked to Mr Johnson earlier in 2019.
But her association with Mr Johnson dates back to when she worked on his successful re-election bid at City Hall in 2012.
Mr Johnson’s union with Miss Symonds will be his third marriage.
Earlier this month, a court heard the Prime Minister and his second wife Marina Wheeler were preparing to end their marriage after reaching an agreement over money.
A family court judge approved a financial settlement and gave Ms Wheeler permission to apply for a divorce decree.
Ms Wheeler and Mr Johnson, who have four children, separated in 2018 after marrying in 1993.
The couple announced that they had separated in September 2018.
Mr Johnson met his first wife, Allegra Mostyn-Owen, while they were students at Oxford.
They married in 1987, but the marriage was annulled in 1993.
Former Scottish Conservatives leader Ruth Davidson was one of the first to congratulate the Prime Minister on the news that he and fiance Carrie Symonds are expecting a child.
The MSP wrote: “Congratulations to Boris Johnson and Carrie Symonds.”
Ms Davidson, who had been critical of Mr Johnson during the European referendum campaign, stepped down as Scottish leader last year to spend more time with her young family.