The actress and her boyfriend Sean Friday were spotted supporting the 25-year-old as she took the stage at The Sayers Club nightclub in Hollywood to sing a cover of songs on Tuesday night.
"Demi looked so proud watching Rumer's set. Rumer wore a deep-V, long black dress and sang about five songs," a source tells E! News. "The set was very soulful, and the crowd was really into her performance."
Rumer even took on a Miley Cyrus hit!
"The crowd went wild when she covered 'Wrecking Ball' as the last song. Rumer and the band were really talented, and it was obvious Demi was really proud of Rumer. She was watching Rumer intently, and smiling as she performed. Demi would clap after each song, and was focused on watching Rumer perform," the source adds.
"Love this girl @stephmatson thank you for coming and supporting my last night @sayersclub#bff#rideordiefriends," Willis wrote with a photo of her and a friend after her performance.
And although Moore was accompanied by her beau, her main focus was cheering on her daughter.
"She looked comfortable with Sean, as they sat and enjoyed the set. They'd say a few words to each other in between songs, but it was clear Demi was there for Rumer," our insider noted, and mentioned, "Demi was wearing little makeup, but was glowing watching Rumer. Rumer was really comfortable on stage. Her voice was powerful. In between songs she'd laugh at her friends in the front cheering her on. She was having a good time!"
Demi was spotted getting very close to her 27-year-old tattooed drummer boyfriend during their recent group vacation in Tulum, Mexico.
"Demi was very comfortable and happy spending every moment she could with Sean," a source had told E! News. "The first day she went and got them towels and they laid down together on a beach bed and cuddled all day long. When they were sitting up, they put their arms around each other or she sat in his lap and whispered in his ear. She was sipping a can of Red Bull and smiling at Sean as she sat with her arms around him and couldn't stop laughing."
"She seemed so in love and happy," the source added. "She loved the attention and seemed very confident."