"Summer of '69" singer Bryan Adams joined fellow Canadian Justin Bieber onstage Tuesday to perform "Baby" -- Bieber's monstrous 2010 hit that is also the most-disliked video on YouTube with 5 million thumbs-down (and 1.2 billion views).
Adams, 55, and Bieber, 21, tackled the surprise duet in Berlin, Germany, during Universal Inside, an intimate Universal Music Group event at Mercedes-Benz Arena. Bieber took the lead, with a vocal assist from a guitar-toting Adams during the chorus.
Earlier this month, Bieber's "What Do You Mean?" debuted at No. 1 on Billboard's Hot 100, making him the youngest male to accomplish the feat. The song also broke Spotify's record for most streams in a debut week.
"Baby" (below) catapulted Bieber into superstardom five years ago. His career launched on Jan. 19, 2007, after his mother uploaded a YouTube video of him performing Ne-Yo's "So Sick." Usher signed Bieber to a record label the following year.