YouTube's 'Proud to Play' commercial is an uplifting, inspiring ad set to celebrate all of the proud gay and lesbian athletes who have come out over the years, including Olympian Tom Daley, football star Michael Sam and NBA player Jason Collins. As the commercial infuses motivational clips of superstar athletes with heartwarming speeches from Nelson Mandela and President Obama, familiar notes from a certain anthemic track play in the background. What's the song?

The awe-inspiring song is none other than Katy Perry's 'Roar,' a tune which is all about believing in yourself, standing up for yourself and letting your true colors show -- a perfect fit for the brave, heartfelt ad. 'Roar,' from Perry's latest album, 'Prism,' hit the No. 1 spot on the Billboard Hot 100, staying in the top spot for two weeks and becoming one of the best-selling singles of all-time.

Check out the heartfelt commercial above, and listen to the full version of Katy Perry's 'Roar' below.