The 26-year-old singer attended the "Genie In a Bottle" crooner's opening night of her Las Vegas residency, TheXperience, at the Zappos Theater inside Planet Hollywood Resort & Casino on Friday night -- and fangirled throughout the entire show.
"The f**king queen herself. A PERFECT, perfect show," Lovato wrote on her Instagram. "Couldn’t believe it was opening night because it was so smooth, flawless and sounded incredible. I was entertained the entire time and was so bummed when it was over until I was reunited with this beauty."
"I’m so so happy I got to hug you @xtina, haven’t seen you in concert since I was 14 and I can’t believe how much life has changed since then," she added. "Honored to call you a friend ? keep it up queen. Oh and EVERYONE should go see #TheXperience at @phvegas!!!"
"[She's] such an admirable young female who is figuring her own stuff out and knowing how to be strong and pull through," Aguilera said about Lovato in an interview in January. "Everybody has their own things they go through, and I just am so proud of her and I just think she’s so adorable and such a talent, such a fierce talent."
ET had sat down with Aguilera earlier this year, where she opened up about what fans can expect at the Vegas show, and her decision to commit to a residency.
"I was like, 'I can see why people are into the residency, because the travel and everything, picking up and tearing it up, putting it back up, all of it [is a lot of work]... to be sort of stationary, you get this great opportunity to build whatever fantasy and whatever kind of show you want," she said.