The 38-year-old 'Late Night' host is said to have "overjoyed" to become a father, reported Contactmusic.
Fallom has been married to Nancy for almost six years.
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Fallom is also the partner of production company Flower Films with actress Drew Barrymore, who happens to be his good friend.
He is set to be replaced on 'Late Night' by Seth Meyers but will begin hosting NBC's 'The Tonight Show' from next year.