On Wednesday, Rathbone -- who welcomed his first child with girlfriend Sheila Hafsadi in July -- tweeted a sweet photo of his Twilight costar Reed, 24, holding his sleeping son.
"Lil Monroe VI with his Godmother . . . Adorable!" the actor, 27, wrote.
Earlier this year, Rathbone opened up to Us Weekly about finding out that Hafsadi -- whom he met on a tour stop while performing with his band -- was expecting.
"One of the greatest things I could expect to be in life is a father," the 100 Monkeys musician told Us. "I'm very excited!"
Rathbone revealed he looked to his own father for guidance. "I have one of the greatest dads in the world," he gushed. "He's just been giving me amazing advice."
This article originally appeared on Usmagazine.com: Nikki Reed Is a Godmother to Jackson Rathbone's Son, Monroe!