The 32-year-old actor, who played Det. Billy Malone on The CW series, announced Sunday on Instagram that wife Lelia Parma gave birth to son Benjamin.
"It's a new dawn, it's a new day, it's a new life. He's Benjamin Parma Ritter. And we're feeling good," he captioned a photo of himself cradling his baby boy.
Ritter, the son of late actor and comedian John Ritter, married Parma in March 2016 after more than eight years of dating.
The couple hadn't yet met when John died of an aortic dissection at age 54 in 2003.
"They talk about the seven stages of grief, but I think most people who have lost a family member would agree you're constantly going through all the stages," Ritter told Entertainment Tonight in October.
"You're constantly cycling through it."
"It's a lifelong thing and maybe the lows aren't quite as low as they were in the days, weeks and years following, but there are still huge lows," he confessed.
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Ritter is the brother of "Another Period" star Jason Ritter and singer Carly Ritter, and the half-brother of actress Stella Ritter.
Jason was among those to celebrate Benjamin's birth online.
"I couldn't be happier today!" the 37-year-old actor tweeted.
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