Watch Selena Gomez's Surprise Performance at BFF Julia Michaels' Concert

Selena Gomez unexpectedly took the stage with her famous friend to perform their joint track.

For Julia Michaels, one friend knows what it's like. 

The songstress' track, "Anxiety," takes fans through the rollercoaster of it, a feeling her friend and fellow star Selena Gomez understands. The two teamed up on the song, which was released at the start of this year. On Monday night, the gal pals took fans by surprise when they reunited on stage during Michaels' concert at the Fonda Theatre in Los Angeles. 

According to a source, Gomez unexpectedly took the stage during the second to last song of the night after Michaels cued her by saying, "Let's see what Selena thinks about it." The stars proceeded to perform the track together and, in the end, Michaels gave her famous friend a big hug and kissed her on the cheek. The two later got coordinating tattoos together on their hands. 

During the show, Michaels also spoke to the audience about having stage fright before performing at the American Music Awards and told the crowd she wanted to be in this together. She also asked attendees if anyone has depression or anxiety and said they are together breaking the stigma every day.  

In honor of her upcoming 25th birthday, the crowd also did some singing to the tune of "Happy Birthday" for the star. According to the source, Michaels sat on the stage with a huge smile on her face as the audience serenaded her. 

Just days earlier, Gomez helped Michaels celebrate her special day with a '90s prom-themed soirée. "My love, my heart and my soul @juliamichaels," Gomez wrote of her beloved friend. 

As Michaels responded, "The amount I love you is unreal."

Ok, we need a tissue. 

—Reporting by Amanda Williams