Watch Taylor Swift Lip-Sync 'Treat You Better' for Shawn Mendes' 18th Birthday!

Taylor Swift rocks some denim overalls while heading out to run errands on Monday afternoon (August 8) in New York City.

That same day, the 26-year-old “Blank Space” entertainer posted a very special birthday message for her good pal Shawn Mendes on his 18th birthday!

She took to Instagram Stories to share a cute video of herself lip-syncing to his latest single “Treat You Better.”

“Partying for Shawn‘s bday & international cat day,” Tay captioned the video, which you can watch below.

You may notice, she’s wearing a cat sweater too!

Last year, Shawn opened for Taylor on her successful 1989 Tour.

FYI: Taylor is wearing a Tularosa overall dress.

45+ pictures inside of Taylor Swift out and about in the Big Apple…