"@perezhilton @alyssa_milano She's stunning. I mistakenly thought the absurdity of what I was saying would have ben taken as a joke. #fail," the 43-year-old comedian tweeted Thursday.
Mohr and Milano both attended a December 6 NASCAR event, after which Mohr told radio interviewers that he could tell the Mistresses actress had a baby.
"She was one of the presenters. ... She's very tiny. In height," he reportedly said. "It seems like she had a baby and said, 'I don't really give a [expletive]' ... I read it on her gut."
Milano, who gave birth to a son in 2011, then hit back on Twitter.
.@jaymohr37 So sorry you felt the need to publicly fat-shame me. Be well and God Bless. Please send my love to your beautiful wife.— Alyssa Milano (@Alyssa_Milano) December 26, 2013
"I had thought (incorrectly) in an improvisational moment, that the incongruousness of my statements, when held up to the light of how beautiful Alyssa Milano is, would have been funny given that she is the size of a thimble," he wrote.
"Sometimes comedians go too far. I went too far. I cannot change what I said, but I can assure you that my heart is broken that I hurt her. I am very sorry," he added.
Milano, 41, accepted his apology on Friday.