Phelps and fiancee welcome baby boy

Los Angeles - Olympic swimming superstar Michael Phelps is a proud father of a baby boy, announcing the birth of son Boomer on Saturday via Instagram.

Phelps said fiancee Nicole Johnson gave birth on Thursday night, and posted a picture of himself cradling the infant at Johnson's bedside.

"Welcome Boomer Robert Phelps into the world!!! Born 5-5-2016 at 7:21 pm !!! Healthy and happy!!! Best feeling I have ever felt in my life!!!," Phelps wrote.

Phelps, whose 22 Olympic medals include 18 gold, is gearing up for a Rio Games challenge.

He'll compete at the US Olympic swimming trials in Omaha June 26-July 3 and has said he hopes to be in Rio with Johnson and Boomer there to cheer him on.

Welcome Boomer Robert Phelps into the world!!! Born 5-5-2016 at 7:21 pm !!! Healthy and happy!!! Best feeling I have ever felt in my life!!! @nicole.m.johnson and Boomer both healthy!!! #boomerphelps ?? @boonestudios

A photo posted by Michael Phelps (@m_phelps00) on May 7, 2016 at 10:22am PDT