Check out the clip -- Celine didn't hold back as she started singing along to the rock band's classic "Livin' on a Prayer" Thursday night at the Bruins game against the NY Rangers ... a rare public appearance amid her ongoing Stiff-Person Syndrome battle.

Celine's right in the thick of the action at Boston's TD Garden alongside her twin sons Nelson and Eddy ... when the camera zeroes in on her as she pumps her fists in the air and claps along while singing along to the catchy tune.

Her inner rockstar comes alive in the X clip shared by fan account @celinebible ... she rises from her seat to unleash an air guitar solo that's pure magic.

You can take the girl off the stage, but you can't take the performer outta her!

Celine wasn't just there to watch the game ... she and her sons got the royal treatment from Bruins coach Jim Montgomery, who introduced them to the team for a legendary line-up read.

The icon's ice hockey antics came hot on the heels of her heartfelt tribute on International Stiff-Person Syndrome Awareness Day ... where she thanked her family, team, and fans for all their love and support since her diagnosis.

Celine was diagnosed with SPS in 2022, and she's been fighting tooth and nail to cope with the autoimmune disorder, even pulling the plug on her tour to prioritize her health.

The truth is ... she has her good days, and bad ones too during this battle. Her sister has said at times Celine is suffering and completely immobilized.