Selena Gomez and Julia Michaels got new tattoos to commemorate their friendship.

The "Lose You to Love Me" singer surprised fans during Michaels' concert in Los Angeles on Monday night (November 11) when she hit the stage with her friend to perform their song "Anxiety" live for the first time.

The two then celebrated the moment by getting matching ink backstage after the show. In videos uploaded to Instagram, the pop stars' tattoo artists, London Reese and Brad Reis, can be seen drawing on them with a pen. Though it's unclear what they got, Gomez and Michaels both got tatted on their wrists.

Their matching tattoos also come one day after the "What a Time" hitmaker held a '90s prom-themed party to celebrate her upcoming 26th birthday. Gomez shared photos from the star-studded bash on Instagram, writing, "My love, my heart and my soul @juliamichaels."

"The amount I love you is unreal," Michaels replied in the comments section.

The pair have been friends for quite a while now. Not only have they written multiple songs together, including "Bad Liar" and "Good For You," but their collaboration "Anxiety," which was released in January, means a lot to Gomez and Michaels because it featured both of them opening up about their experiences with anxiety and depression.

Gomez previously discussed it's importance earlier this year, writing, "This song is extremely close to my heart as I’ve experienced anxiety and know a lot of my friends do too. You’re never alone if you feel this way."