The US Olympic swimmer and his wife announced the arrival of their a baby boy named Beckett Richard Phelps via their other son Boomer's Instagram page.
"I am officially a big bro!!!," the captioned read "All I wanna do is hold him! I can’t wait til I get to teach him so many cool things about the world!! #bigbro"
Phelps also shared the news on his own Instagram, posting a photo of his wife holding baby Beckett, with little Boomer cuddling up as well.
"Magical moments yesterday... Nicole and I would like to introduce Beckett Richard Phelps to the world! We had a healthy baby boy and a healthy mama. I truly do feel like the happiest man in the world. Being able to build our family to now 4 (6 with doggies) is so incredible! #familyof4now"