In the no hard feelings department, there apparently aren't any, or many, between Nickelback frontman Chad Kroeger and his ex-wife, Avril Lavigne.

Nickelback feat. Avril Lavigne - Rockstar (Live at the Greek Theatre - 08.09.17)

Nickelback feat. Avril Lavigne - Rockstar (Live at the Greek Theatre - 08.09.17)

Lavigne joined Nickelback on stage on Friday night (September 8), in Los Angeles during the group’s performance of "Rockstar;" Afterwards the group tweeted a photo of Lavigne, Kroeger, guitarist Ryan Peake and a fan named Owen who Peake had pulled out of the crowd with the message, "You never know who will join us for Rockstar karaoke. Tonight we got super lucky with these two rockstars. It just might be you next!"

Nickelback on Twitter

You never know who will join us for 'Rockstar' karaoke. And tonight we got super lucky with these two rockstars. It just might be you next!

It was Lavigne's first performance in three years, according to reports.

She and Kroeger were married from 2013-15, and Kroeger worked on Lavigne's last album, a self-titled effort released during 2013. The two are reportedly still on good terms, and Kroeger told us during the marriage he thinks the world of Lavigne as an artist:

"It was amazing to be able to work with somebody that talented. I knew she could sing, but...I didn't really know until I got in the room with her how well she could sing. Like, the pipes on my wife, they're unparalleled. Like, this girl, for as petite as she is, this tiny little woman has this voice of a trumpet, and it's great to be in a room with somebody like that because there is no note she can't hit, so there's no handcuffing when it comes to writing songs in any key and getting her to do anything you want."

Nickelback is on the road promoting its latest album, Feed The Machine, wrapping up October 1 in the group's home town of Vancouver.

Gary Graff is an award-winning music journalist who not only covers music but has written books on Bob Seger, Neil Young and Bruce Springsteen.