Justin Timberlake Has Been 'Completely Changed' by Fatherhood Lance Bass Reveals: Watch!

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It's an 'NSYNC reunion!

Justin Timberlake and Lance Bass were both at 30 Rock in NYC on Wednesday taping for The Tonight Show and The Meredith Vieira Show, respectively. The two boy band alums even had a little run in, which Lance posted to Instagram, writing, "Well well, look who's in the #NBC house today! @JustinTimberlake and Cousin Rachel! Catch JT on @jimmyfallon!"

WATCH: Justin Timberlake Shares the Cutest Pics of 5-Month-Old Silas

While talking to the Meredith Vieira panel, Lance revealed how Justin is adjusting to fatherhood, saying it has made the pop star a "completely changed" person.

"It's so amazing to see a friend go through this, because you know, I grew up with him, since he was 14 years old," said Lance. "But to see this amazing dad now, and you know, all he wants to talk about is the kid."

Addressing Justin's change, Lance added, "You have to. And you know, I can't wait to be a dad myself, just because I would like to know what that selflessness feels like."

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Of course, it's easy to see why Justin could give someone parenthood goals -- he and wife Jessica Biel's 5-month-old son, Silas, is possibly the cutest little baby EVER. The Tonight Show account tweeted pictures of the little guy, writing, ".@jtimberlake brought baby pics! #FallonTonight."

WATCH: Jimmy Fallon & Justin Timberlake Enjoy Epic Night Out With Kate Hudson and Jennifer Lopez

"It is the most insanely amazing, wonderful, unbelievable thing to ever happen to you," Justin told Jimmy about becoming a father.

After the taping, Jimmy and Justin went to a U.S. Open match together, and showed off their moves in an impromptu dance-off to Beyonce’s "Single Ladies (Put a Ring on It)."

WATCH: Justin Timberlake and Jimmy Fallon Totally Won the U.S. Open With Their 'Single Ladies' Dance

Watch below!