Miley Cyrus joins Reese Witherspoon, Renee Zellwegger and Courteney Cox at ALS walk

Miley Cyrus joined Reese Witherspoon, Renee Zellweger and Courteney Cox for the 13th Annual Country Walk to Defeat ALS on Sunday.

Talk about a star-studded crowd!

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Miley, 22, made a surprise appearance to warm up the 2,000 people crowd to Pharrell William's song Happy, with celebrity pilates instructor Mari Winsor, who is currently battling the disease.

"I'm already sweating. She had us doing a happy warm-up and she kicked my ass once again,” she told E! News. “She's done it for years and she's already done it this morning and it's only 11!"

Courteney Cox, Reese Witherspoon, Nanci Ryder & Renee Zellweger. Photo: Getty

Meanwhile, Courteney, Renee and Reese wore ‘Team Nanci’ T-shirts to support publicist Nanci Ryder, who was diagnosed with ALS two years ago.

"I'm just happy to be here supporting Nanci but also just raising awareness and raising money for ALS,” says Reese, 39, who participated with her husband Jim Toth and 16-year-old daughter Ava.

Reese Witherspoon & Renee Zellweger. Photo: Getty

“There's so much that's not known about this disease and watching our friend progress every single week with something different and not know is so horrible. There are so many families living with this devastating disease.

“It's time that we start doing something to create a cure, to find what the root of the problem is and eradicate it because it's just unbelievably devastating."

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