The former couple walked the carpet together, then cozied up inside the event.
The pair announced their separation in September, but they stood side-by-side Sunday night.
The 31-year-old singer is 'overcoming Lyme disease.'
Keep fighting, Avril!
The exes were "back where it all started" in the recording studio on Saturday.
The singer shared Instagram pics from her doctor's office visit on Tuesday.
Lavigne announced the split via Instagram.
Things got complicated.
The Sum 41 rocker tied the knot with Ariana Cooper at a small, stylish ceremony on Sunday.
There's nothing but mad love between these two.
The singer took the stage for a debut performance of her new single "Fly."
Avril Lavigne breaks down in tears on Good Morning America.
The 30-year-old singer opened up to 'Good Morning America' about her frustrating struggle to get treatment for the disease.
You might get blinded by some of these blinged-out sparklers!