US actress Olivia, 30, gave birth to their son yesterday (23 April) and the couple have named him Otis Alexander.
Announcing their happy news to fans, Olivia tweeted: "Ladies and gentlemen, Otis Alexander Sudeikis has LEFT the building! (I'm the building)."
Alongside the tweet, Olivia shared a gorgeous candid photograph of herself cuddling Otis, who is wrapped in a cosy blanket.
OC actress Olivia announced in October that she and Jason were expecting their first child together, joking: "Babies eat mostly salsa right?"
Since then, Olivia has been keeping fit with gentle pilates workouts and showing off her baby bump on the red carpet.
Earlier this month, Olivia had hinted that her baby was due on 4 May - but he obviously couldn't wait until then to meet his mummy and daddy!
Couples who have welcomed babies in 2014:
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