Michael Phelps' new post-swimming gig: Running his son Boomer's Instagram

Just when we thought Michael Phelps couldn't get any cooler, he dropped this bomb during an appearance on "The Tonight Show": He's the voice behind his son Boomer's adorable Instagram account!

The tot went from 5,000 followers in late June to a whopping 672,000 at current count — a rise that Phelps laughed about with Jimmy Fallon.

"It’s insane," Phelps said. "He’s got to be the most followed baby in the world!"

While Phelps says the account is a team effort — fiancée Nicole Johnson takes most of the photos — he maintains that he's the brainchild behind Boomer's witty words.

Mom these head bands are sweet!!! #headbandgamestrong

A post shared by boomer phelps (@boomerrphelps) on

As for his son's unique name, Phelps says he and Johnson were really looking for something different.

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"We heard the name and we didn't want a normal name," he told Fallon. "I brought it up to Nicole and she was like 'oh, that sounds kind of cool.""

After Boomer's rise to internet fame, the couple has no doubts about his future.

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How did Michael Phelps spend his first day after Rio? In the pool, of course!

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How did Michael Phelps spend his first day after Rio? In the pool, of course!

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"He's definitely going to be the cool kid," Phelps joked.

When he's not running Boomer's Instagram account, Phelps has been spending time volunteering for the Arizona State University swim team, traveling, golfing and getting ready to tie the knot with Johnson.

Watch out @mattlauernbc and @carsondaly I'm coming for ya!! @todayshow

A post shared by boomer phelps (@boomerrphelps) on

Oh, and if you're wondering about the larger-than-life-size cutout behind Phelps' chair, Fallon presented it to the swimmer as a gift earlier in the show.

The hashtag #PhelpsFace went viral during the 2016 Rio Olympics when the swimmer was photographed staring down opponent Chad le Clos before the 200-meter butterfly semifinals.

We're sure Phelps is only smiling around baby Boomer!