Selena Gomez and Julia Michaels took their friendship to the next level and sealed it with matching tattoos on Monday.

Ahead of Julia Michaels's birthday on Wednesday, the pop-pals got matching tattoos of an arrow on their lower thumbs. Sharing a candid picture of them from the tattoo parlour on Instagram stories, Selena wrote, "It's tatted.. my arrow points to you forever."

The "Fetish" singer also shared several pictures of her and the "Issues" star getting inked at The Black Lantern Studio. Artist London Reese in a post on Instagram revealed he tattoed Mixhaels while one of his pal Brad Reis tattoed Selena Gomez. The artist also shared a video of the two friends getting tattoed, reports E! News.

"Spent the last couple days celebrating the birth of one of my faves, miss @juliamichaels. Went to her show with @bradreis_tattoo and I tattooed Julia while Brad tattooed the ever so sweet @selenagomez. The vibes were the sickest and both these girls are as dope as you could hope for. Happy birthday, Feej! Love ya, kid!!," Reese wrote on Instagram.

Gomez has been celebrating her BFF's birthday for quite a few days now. On Monday night, the 27-year-old stunned everyone during Michaels concert at the Fonda Theatre in Los Angeles. The "Look At Me Now" singer unexpectedly got up on stage to perform the second-to-last song of the night with her best friend. Before the performance, Michaels reportedly told the crowd, "Let's see what Selena thinks about it."

The BFFs selected song "Anxiety" for their performance at Fonda Theatre, a duet they dropped earlier this year. Sharing the experience of singing on-stage together, Michaels wrote on Instagram, "I'm kind of convinced these last few days aren't real. Thank you @selenagomez for the most epic headline show I've ever played."

Selena Gomez
Selena Gomez attends the 2017 American Music Awards at Microsoft Theater on November 19, 2017 in Los Angeles, California. (Photo by) Neilson Barnard/Getty Images

The singer who turned 26, wrote for her friend, "I love you beyond words and I'm so happy we finally got to sing our baby together."

Gomez also played dress-up for her BFF's pre-birthday bash. The "Same Old Love" singer wore black Kiki De Montparnasse dress for the 90s prom-themed celebration.