"I've been married for a while," he said. "A couple months. I had to keep it a secret from y'all. I had to keep it hush-hush from you guys."
When one viewer asked why he didn't go public with the marriage, he answered, "Just because." The superstar athlete gave interviews after the Olympics and discussed looking forward to his future wedding.
Then Phelps hinted that a infant son Boomer may be getting a little brother or sister.
"Thank you for the beautiful comment," Phelps said. "Baby number two may be coming soon. Who knows, though?"
Phelps and Johnson got engaged in February 2015. Johnson gave birth to their son, Boomer, in May.