The Backstreet Boys joined by members of NSYNC during Vegas residency

What rivalry? NSYNC member Lance Bass joined the Backstreet Boys on stage March 18.

The popular 90's boy band serenaded Bass at their Las Vegas residency show at Planet Hollywood.

Every '90s fangirl in the world may actually watch this video and burn with envy of Bass as he stands there all smiles.

They shared the sweet moment of their performance to "Shape of My Heart," which ended with so many hugs amongst the guys.

"We really showed @lancebass the shape of our hearts tonight. Thanks for coming by #BSBVegas, brother!" read a message posted on the group's Instagram page.

However, he wasn't the first NSYNC member to be chosen for this honor. Joey Fatone joined them earlier this month. Heck he even kissed Nick Carter.

The shape of our heart is no longer existent, as it is in a puddle on the floor watching this.