Michael Phelps is going to be a daddy.
The 18-time Olympic gold medalist announced Wednesday on his Instagram and Twitter accounts that his fiancee Nicole Johnson is expecting their first child. In February, Phelps used the same platforms to reveal his engagement to the former Miss California.
Phelps' agent confirmed the news of the swimmer's impending fatherhood.
Phelps posted a photo of him and a smiling Johnson standing poolside in Arizona holding tiny black swim trunks with the initials `MP' on it.
''We found out 8 weeks ago we are expecting,'' the caption says. ''Today we're over 12 weeks and it looks like we're having a boy!!!''
Phelps has said he and Johnson, both 30, would marry after next summer's Rio Olympics. He's in training to compete in his fifth games after coming out of retirement in 2013.
Based on Phelps' announced timing, Johnson is due to give birth next spring. The U.S. trials to decide the team for Rio are June 26-July 3. The Olympics begin Aug. 5.
The baby will be Debbie Phelps' third grandchild.
In August, Phelps relocated from his hometown of Baltimore to Tempe, Arizona. He trains with longtime coach Bob Bowman, who took over as coach of the Arizona State swimming program.
Earlier this year, Phelps completed a six-month suspension by USA Swimming after a second drunken driving arrest in 2014. In last week's Sport Illustrated, he discussed his time in alcohol rehabilitation and how he thought about ''not wanting to be alive anymore'' after his arrest.