Boris Johnson appeared flustered when asked if he will be changing nappies when his new baby arrives.
The Prime Minister and fiancee Carrie Symonds are expecting a child in the early summer.
Appearing on ITV's This Morning, host Holly Willoughby told the Prime Minister: "We can't let you go without saying congratulations."
— This Morning (@thismorning) March 5, 2020
Mr Johnson admitted he was "very excited", but did not add anything else, prompting co-host Phillip Schofield to ask: "Is that it?"
When asked: "How good are you at changing nappies? Will you change nappies?", the Prime Minister appeared flustered before eventually saying: "I expect so."
He would not answer when asked how the rest of his family are taking the news, and when Schofield questioned him on his reticence to discuss his personal life, saying: "All family life is happening in Downing Street and you won't talk about it," Mr Johnson replied: "Very sensibly."
He added: "I've spent an awfully long time deliberately not going on about it, for the very good reason that there are people that I love that I don't want to put in the debate and that's the reason."
On the nappy question, he said: "That was a very tricky one, there was nowhere to go on that one."
Over the weekend, Ms Symonds 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.