British Prime Minister Boris Johnson and his partner Carrie Symonds announced their engagement on Saturday and said they are expecting a baby later in the year.
A spokesperson for the couple said the couple are "very pleased" to make the announcement.
Johnson, 55, and conservationist Symonds, 31, became the first unmarried couple to occupy Downing Street when they moved in last year.
"The Prime Minister and Miss Symonds are very pleased to announce their engagement and that they are expecting a baby in the early summer," the spokesperson said.
Symonds is also the youngest partner of a UK Prime Minister in 173 years.
Talk of a Downing Street wedding bells had gathered momentum after it emerged in court documents earlier this month that Johnson and his Indian-origin ex-wife Marina Wheeler had agreed a divorce settlement.
The details of the financial settlement have not been made public.
Johnson and Wheeler, who married 25 years ago before their separation last year, have four grown-up children Lara, Milo, Cassie and Theodore.
This will be Johnson's third marriage. He met his first wife, Allegra Mostyn-Owen, while they were students at Oxford University and they married in 1987.
The marriage was annulled in 1993 and he wed Wheeler later that year.
The last child born to a sitting UK prime minister belonged to David and Samantha Cameron, who welcomed Florence Rose Endellion into their family in August 2010.
Symonds met Johnson during her time as the communications chief for the Conservative Party.
She now works for an ocean conservation charity and it was recently reported that she had appointed her own Downing Street aide akin to a First Lady.
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