"Dancing With The Stars" has announced its fourth cast member for the upcoming season, and it's Vine and YouTube star Hayes Grier!

The 15-year-old Internet sensation officially announced Thursday that he would be joining the hit show in a video on Twitter. "Hey guys I made my big announcement a little early," he wrote. "Go watch the video! Hope you will support me through this!"

In the video, a groggy Grier, who makes sure to point out that it's 4 a.m. in Los Angeles, says how he initially thought he had to wait another week to share this news, but he had gotten a call that he could go ahead and announce it now. "It's going to be really cool and an amazing journey to be on season 21 of 'Dancing With The Stars,'" he says. "And I'm super excited."

Grier, who many people know as the brother of Vine star Nash Grier, will be the second-youngest star to ever compete on the show, according to Entertainment Weekly. In season 20, Willow Shields from "Hunger Games" competed at just 14. With 4 million Vine followers, 2.93 million Twitter followers and 4.1 million Instagram followers, it's obvious that he has a huge fan base on social media to help him throughout this journey. He even asked his fans to send him their best dance videos.

He is the fourth star to be announced so far, joining Bindi Irwin, Victor Espinoza and Nick Carter on the dance floor. According to Grier, the tough rehearsals have already begun. "I'm going to go back to bed right now since I have my first rehearsal in a few hours," he tweeted. "Keep the hashtags going and trending! Be back soon."

The official "DWTS" Instagram page even shared a photo of his dancing shoes, showing just how ready he is to take on this challenge. "@hayesgrier just couldn't wait to get into his dancing shoes!" they wrote.

Stay tuned for more cast updates and see the full reveal on "Good Morning America" on Wednesday, Sept. 2. "DWTS" premiers Sept. 14 on ABC.

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