Michael Phelps Celebrates Son Boomer's First Birthday: Photo

Time to blow out the candles, Boomer! Michael Phelps and his wife, Nicole Johnson, are celebrating their son's first birthday on Friday, May 5.

In honor of the big occasion, the 23-time Olympic gold medalist, 31, posted a throwback photo of the day Boomer was born.

"One year ago.. @mrs.nicolephelps and I had the privilege to welcome @boomerrphelps to this world.... for me it's the best thing that ever happen to me!!" Phelps captioned the Instagram pic.

Hours earlier, Johnson, 31, listed some of Boomer's latest milestones. "On and off his cars, in and out of his wagon, climbing on everything but also turning around to get down," she wrote via Instagram. "Drinking from his own cup. Making a drum out of anything. Clapping when he hears an audience clap. And so much more... Happy Early Birthday to the most special gift we could have ever asked for @boomerrphelps."

Phelps and Johnson secretly tied the knot in June 2016 after dating on and off for eight years. In October, the athlete teased about expanding their family. "Baby number two may be coming soon," he said in a Facebook Live video at the time. "Who knows, though?"

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