Boris Johnson indicated he would “almost certainly” be taking paternity leave when his new baby arrives.
The Prime Minister and fiancee Carrie Symonds are expecting a baby in the early summer.
Asked whether he intended to take time off, Mr Johnson said: “The answer is almost certainly, yes.”
Although as he then suggested “I can’t remember what the question was”.
Over the weekend Ms Symmonds told her followers on Instagram she felt “incredibly blessed”.
She said she and Mr Johnson got engaged at the end of last year “and we’ve got a baby hatching 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.
The new arrival will be the third baby born to a serving prime minister in recent history.
Tony Blair’s wife Cherie gave birth to son Leo in May 2000, three years after her husband’s first election victory.
Conservative prime minister David Cameron and his wife Samantha welcomed daughter Florence Rose Endellion Cameron in 2010, three months after Mr Cameron had formed a coalition government with the Liberal Democrats after that year’s general election produced a hung parliament.
The last babies born to prime ministers before Leo and Florence arrived more than 150 years ago.