Looks like Michael Phelps scored more than gold medals this summer. The Olympian can add getting married to his long list of accomplishments this year.

TMZ Sports reports the 31-year-old swimming champion secretly married longtime girlfriend Nicole Johnson on June 13, a little more than a month after the former Miss California USA gave birth to their son, Boomer.

The site posted a copy of a marriage license that shows Phelps and Johnson were married in Paradise Valley, Arizona. Neither Phelps, nor Johnson said anything about the wedding. Johnson posted a picture of her with Phelps and Boomer on Instagram on the day of the ceremony with the caption, "Such a memorable night with my lil fambam."

Phelps won five more gold medals in this year's Rio Games to increase his overall haul to 23.

The Associated Press contributed to this report.