Michael Phelps dives into gene pool, becomes father

In this file photo, Michael Phelps smiles as he warms up before the upcoming Charlotte Grand Prix swimming event in Charlotte, N.C., Thursday, May 15, 2014. (AP Photo / Chuck Burton)

Michael Phelps is a first-time father.

The 18-time Olympic gold medallist and fiance Nicole Johnson welcomed Boomer Robert Phelps late Thursday in Arizona, where Phelps has been training in preparation for the Rio de Janeiro Olympics.

"Healthy and happy!!! Best feeling I have ever felt in my life!!!" Phelps posted on Instagram on Saturday in announcing his son's name and arrival date and time.

A black-and-white photo showed a shirtless Phelps cradling his son and planting a kiss on his head while Johnson looked on from her hospital bed.

Phelps had been training at high altitude in Colorado, and left the Olympic Training Center in Colorado Springs to return to Johnson's side.

Last month at a meet in Mesa, Arizona, Phelps said the couple had already selected the baby's name, although he didn't reveal it then.

"It's something we both agreed on, thought it was different," he said.

Asked what type of parent he would be, Phelps said, "I'll probably be very protective. That's how I am."

Phelps credited Johnson for being "nothing but one of the best supporters I could ask for."

At the Mesa meet, Phelps talked with Dana Vollmer, who is attempting to make another Olympic team after giving birth to her son 13 months ago.

"It will be good for him, like it is for me," she said. "Michael and Nicole will be good parents."