Actress Minnie Driver looked so authentic as a mother-to-be in an upcoming movie, her four year old son was convinced a sibling was on the way.

The British star wore a prosthetic baby bump for her role in Return to Zero, but when her real life son Henry saw her bulging figure he couldn't wait for a brother or sister - and he even offered to be his single mum's suitor during her 'pregnancy'.

Driver tells U.K. talk show host Graham Norton, "It was weird being knocked up again. What I liked about it was when I was really pregnant I was the size of a house, but this was how every woman imagines she would look with the perfect neat bump...

"I had to explain (to Henry) I was pretending to be pregnant and he was like, 'Are we having a baby?' He was genuinely waiting for there to be a baby and was very keen. When he said he wanted a brother or a sister I explained, 'You need a boyfriend or husband to have one of those,' and he said, 'Ah, I can be that.'"