Shawn Mendes and Justin Timberlake perform onstage during the 2018 iHeartRadio Music Festival at T-Mobile Arena on September 22, 2018 in Las Vegas, Nevada.

Justin Timberlake was already owning the iHeartRadio Music Festival stage with his epic opening set when he asked the crowd, "Can I do something special for you tonight?"

Of course the answer was yes, and he didn't disappoint with his special guest. "Ladies and gentlemen, I'm a big fan of this young man," Timberlake said, milking the introduction. "He's one of the coolest cats I've met, he's very talented, and he's about to bless you -- please welcome Shawn Mendes to the stage."

Mendes hit the stage, guitar in hand, to help JT with "What Goes Around...Comes Around," slowing down the already-downtempo song for an especially dramatic, gospel-like take on the FutureSex/LoveSounds single. The "In My Blood" singer took over the second verse, perfectly matching Timberlake's pleading vocals.

Shawn Mendes cantando “What Goes Around... Comes Around” com Justin Timberlake hoje no iHeartRadio Music Festival em Las Vegas, Estados Unidos.pic.twitter.com/6jQ0zczCpD — Portal Shawn Mendes--? (@PortalSMBRA) September 23, 2018

The duo ended the song with a line from Timberlake's Chris Stapleton collaboration "Say Something," and as Mendes exited the stage, the band picked up with the Man of the Woods standout.

Timberlake performed a full set to open day 2 at Las Vegas' T-Mobile Arena, kicking things off with the pumping beat of "Filthy" and leaving the crowd dancing with "Can't Stop the Feeling!," and a pack of hits in between. Find his full set list below:

Filthy

LoveStoned/I Think She Knows

SexyBack

Man of the Woods

Higher Higher

Senorita

Cry Me a River

Mirrors

What Goes Around...Comes Around (with Shawn Mendes)

Say Something

Can't Stop the Feeling!

iHeartRadio Music Festival day 2 continues with a full set from Mendes, plus fellow performers Kelly Clarkson and Imagine Dragons.