Olympic swimming champion Michael Phelps after her fiancee Nicole Johnson delivered a baby boy.

The news of baby's arrival was revealed by Phelps on Instagram. "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!!!," he wrote.

The 30-year-old Phelps is training for the United States Olympic trials that will be held from June 26-July 3.

It may be recalled that Phelps retired after the 2012 London Olympics, but returned to the pool after two years.