Boris Johnson and Carrie Symonds have announced the birth of a “healthy baby boy at a London hospital earlier this morning”.
A spokesman for Boris Johnson and Carrie Symonds said: "The Prime Minister and Ms Symonds are thrilled to announce the birth of a healthy baby boy at a London hospital earlier this morning. Both mother and baby are doing very well.
"The PM and Ms Symonds would like to thank the fantastic NHS maternity team."
The birth comes two days after the PM returned to work after recovering from Covid-19, which saw him separated from his partner while he spent time in hospital, including a period in intensive care.
Health Secretary Matt Hancock said he was "thrilled" for the pair following the birth. While Labour leader Sir Keir Starmer said it was "wonderful news."
The relationship between the PM and Ms Symonds came to public attention at the beginning of 2019, a few months after Mr Johnson separated from his then-wife Marina Wheeler.
Johnson, 55, and Symonds, 32, announced in March that they were expecting a baby in "early summer", and that they had become engaged at the end of last year.
In a post on her Instagram account, Carrie Symonds wrote: "Many of you already know but for my friends that still don't…. we've got a baby hatching early summer."
Johnson said he was "absolutely delighted" as the news was made public on March 1.
The announcement came just 11 days after Mr Johnson's divorce with ex-wife Marina was finalised.
Johnson has previously suggested he intends to take paternity leave, although it is not known if this remains the case given the coronavirus crisis.
He will not appear at Prime Minister's Questions in the Commons on Wednesday afternoon.