Michael Phelps cried when he saw this commercial about his final Olympics

After a turbulent career as the greatest swimmer in history, Michael Phelps has promised that this summer's Olympic Games in Rio de Janeiro will be his last.

Five months ahead of the games, Under Armour is already celebrating 18-time gold medalist's last hurrah with a stirring new commercial that offers an inside look at the intense training regimen behind all of those world records.

The 90-second spot, which debuted at an event in Phelps' hometown of Baltimore this week, is part of the sportswear brand's ongoing "Rule Yourself" campaign, which puts a spotlight on all of the grueling hard work that comes before the nail biters and winning celebrations that most people ultimately see on TV.  

Its tagline: “It’s what you do in the dark that puts you in the light.”

Along with the commercial, Under Armour also released a video of a tearful Phelps and his fiancee reacting to the ad during a visit home in December.

"That's insane," Phelps says after viewing it for the first time.

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Of course, Phelps made the same promise about the 2012 Olympics, then jumped right back in the pool to train again afterwards, so his vow is best taken with a grain of salt. 

With the help of ad agency Droga5, Under Armour's campaigns with high-profile stars like Steph Curry and Dwayne "The Rock" Johnson have boosted its profile and made it a fast-growing rival to athletic giants like Nike and Adidas.

In a mostly negative Morgan Stanley report last week, an analyst said that the one caveat to his pessimistic outlook for the company's stock could be its endorsement from Curry, which is estimated to be worth $14 billion.

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