The pop star-turned-actor grew up with Gosling and the two castmates even lived together as their TV careers took off - and Timberlake is very proud of his pal's success.
He says, "He's unbelievable, I think one of the best actors of our generation... He is working a lot too. It's hard to keep up with him."
And the 'In Time' actor tells Ellen DeGeneres he has very fond memories of hanging out with Gosling when the two pre-teens were on the verge of stardom.
He adds, "His mother had to keep her job in Canada the second year that we were on the television show and my mom was his guardian for, like, six months, so we actually lived together.
"We were probably a little closer than the rest of the kids that were on the show just because we had to share a bathroom.
"We used to do terrible things. We thought we were so cool when we were on the Mickey Mouse Club. Looking back on them, they weren't as bad as I thought they were at the time. We stole a golf cart. And we we're like, 'Yeah, man. We're stealing a golf cart...' but... it's, like, on a backlot; there's golf carts everywhere.
"We stole the golf cart and we drove into MGM Studios, which is totally illegal by the way... We went and got milkshakes."
Justin and Ryan were definitely two of our favorite Mousketeers. Who didn't love their performance of "Cry for You" from the MMC? If you haven't seen it, or you just want to again, check it out below. Justin's episode of the Ellen DeGeneres Show airs Thursday on NBC.