Simon, who is best known for his roles in The Inbetweeners and Friday Night Dinner, and his wife Lisa Owens, actually welcomed a son six months ago, but the beans were only spilled during a recent interview with Simon's Friday Night Dinner co-star, Tom Rosenthal.
Speaking to Heat magazine about his new TV show, Flat TV, Tom said, 'Simon very cleverly watched it only after we finished filming Friday Night Dinner, because if he didn't like it, that would have made things very awkward.'
'It would be like me saying his kid is s**t.'
'Luckily, his kid is actually bloody great. He's got this bobbing head. And he's got this 'Simon Bird' slightly judgmental air about him.'
Simon then confirmed the news himself, adding, 'He is quite judgemental. He's six months.'
'He's only six months old but I feel like he's already patronising me. It's great,' Tom quipped.
Simon and Lisa met during their time at Cambridge University and married in 2012, after Simon proposed in Paris the previous year. The pair have not yet revealed the name of their son.
Simon pictured with his fellow Inbetweeners, James Buckley, Blake Harrison and Joe Thomas
Simon isn't the only member of the Inbetweeners clan that's become a father - Blake Harrison, who played Neil, has had a baby, and James Buckley, who played Jay, and his wife Clair have two sons, Harrison and Jude.
Speaking to The Sun around the time of Harrison's birth in 2011, Simon said of his co-star's son, 'We met the little b**tard the other day and he is a little b**tard, technically' (as James and Clair were not married at the time).
'But I can honestly say he's the cutest thing I've ever seen in my life - he's really sweet.'