Britney Spears kicked off her two-year residency at Las Vegas' Planet Hollywood, and Miley Cyrus was front row the first night, dancing along every step of the way. Huh, she must know someone. (Joking! Brit is a featured collaborator on Miley's Bangerz album.)

Miley was super excited for the show, as evidenced by the backpack she wore to the venue and the following tweet:

Later, a few fans caught the "Adore You" singer completely geeking out during "Till the World Ends," the lead single off of Brit's Femme Fatale. Check out the Instagrams below.

As for why Miley was so pumped to see the 32-year-old pop star on opening night, Miley's retweet of a fan account explains the whole thing: "Britney is to Miley what Miley is to us."

Full circle... or something.