Lady Gaga labeled Selena Gomez "the biggest rockstar of the night" after her brave speech at the American Music Awards on Sunday (20Nov16).

The popstar was not expected to attend the ceremony in Los Angeles and so her arrival on the red carpet was a shock to many, marking her first public appearance since she abandoned her world tour this summer (16) and reportedly checked into rehab to focus on her struggle with autoimmune disorder lupus.

Gomez previously cut short a 2014 tour of Australia and checked in to the Dawn at The Meadows facility in Arizona to receive professional care and undergo chemotherapy. In August (16) she announced she was taking an indefinite break from her world tour in order to focus on getting well again.

"I had to stop because I had everything and I was absolutely broken inside," she said during her AMAs speech. "I kept it all together enough to where I'd never let you (fans) down, but I kept it too much together, to where I let myself down.

"All I can say from the bottom of my heart is I am so grateful that I have the opportunity to be able to share what I love every single day with people that I love... If you are broken, you do not have to stay broken."

Following Selena's emotional speech, stars flocked to social media to lavish praise on the 24-year-old singer.

Gaga shared a snap of herself with Selena on her Instagram page, writing: "So dope I got to hang with the biggest rockstar of the night.(Ya,know besides Sting and Green Day) …the girl with the biggest prize of all a BIG Heart that she shares with the world."

Fifth Harmony singer Camila Cabello shared a clip of Selena's speech on her Twitter page, writing: "I love you".

Fall Out Boy's Pete Wentz tweeted, "Selena speech at the amas (heart emoji) more of that in the world please," while actor Colton Haynes wrote, "Sendin the biggest hug in the world to @selenagomez for speaking about how important it is to take care of your mental health."

Selena's BFF Taylor Swift is reported to have taken to her social media as well in the wake of the singer's speech, sharing a video of herself screaming as the stunning brunette took to the stage. "Baby", she is said to have captioned it, according to fans.