Britney Spears joins TikTok 'Toxic' trend to celebrate boyfriend's birthday

Britney Spears celebrated her boyfriend Sam Asghari's 27th birthday by putting her own spin on the now-viral "Toxic" challenge taking over TikTok.

The challenge tasks TikTok users to press their faces against a glass surface and make shrill wiping noises after Spears sings "Do you feel me now?" in the pre-chorus.

Well, it was only a matter of time before the pop princess herself joined the challenge -- and roped Asghari along for the ride.

"Happy birthday to the man that always makes me laugh," wrote Spears, who shared side-by-side videos of the two wiping their faces across the glass shower door. "Who did it better????" Swipe to see both videos:

Spears poses seductively in her massive shower while wearing nothing but a robe and, when the time comes, playfully swipes her face across the glass door.

Asghari's attempt at the challenge is a bit more dramatic, as he rises from the shower's bench and twirls to the door before he, too, rubs his face all over the glass.

It is obvious the two -- who first met in 2016 when filming Spears' "Slumber Party" music video -- enjoyed the silly challenge as they both broke out into wide smiles and started laughing right after.

Spears released "Toxic" on her fourth studio album, "In the Zone," in 2003. The song won her the Grammy that year for Best Dance Recording.