Scroll through to see their love through the years, and don't forget to check out even more adorable celebrity couples!
He was 16 and just starting out in 'N Sync, she was 23 and one-third of the pop trio, Wild Orchid -- talk about robbing the cradle! They grew up together on the Disney show, and began a romance in 1999.
"It was before he got real heavy with Britney," she told Australia's . It all came crashing down in 2002 after Brit allegedly cheated on him, which inspired his hit song "Cry Me a River" off his debut album, in 2011."We spent way too much time being the biggest thing for teenyboppers." She starred as his love interest in his racy music video for "What Goes Around... Then he was spotted visiting her apartment in 2011 (during his brief split from Jessica Biel -- more on that later). That's something only the two of them know since they've never publicly discussed it!
And in those awesome/talented/swoon-worthy years, the birthday boy has wined and dined a lot of Hollywood ladies.
To honor JT's special day, we're taking a look back at all of his high-profile romances.
In her film debut, Biel played the character Regrettal, a lead role in the ambitious musical film titled It's a Digital World, produced and directed by Paul Greenberg.
At the age of fourteen, after auditioning for several television pilots, Biel was cast as Mary Camden, the second oldest child in the family drama 7th Heaven.In 2006, Biel played a turn-of-the-century duchess in the period piece The Illusionist, co-starring Edward Norton and Paul Giamatti.While her casting was met with a mixed response, her performance was ultimately praised.She then played in the summer comedy, I Now Pronounce You Chuck & Larry, co-starring Adam Sandler and Kevin James. At the start of 2008, Biel shot Easy Virtue, an adaptation of the play by Noël Coward.In late 2007, Biel signed on to play a stripper in Powder Blue, alongside Forest Whitaker (who also produced the film), Ray Liotta and Patrick Swayze. Like the play, the film is set in the 1920s and Biel plays young widow Larita, who impulsively marries John Whittaker in France and must face her disapproving in-laws on returning to England.Justin and Jessica first took their relationship public in January 2007, shortly after the singer split from actress Cameron Diaz.