Michael Phelps I'm A Dad!!

Michael Phelps just got the final product of his very own swimmers ... he's now the proud dad of a new baby boy.

Phelps posted the pic Saturday welcoming Boomer Robert who was born Thursday night. You can also see Phelps' fiancee Nicole Johnson in the background who Michael says was healthy and feeling good post-baby.

Add raising a new kid to Phelps' list of responsibilities ... he's got the Olympics coming up in just a few weeks.