A 来源 tells Us Weekly that Osbourne rented out Beacher's Madhouse inside the Hollywood Roosevelt Hotel to help the 19-year-old celebrate her special day.
"Her mom Tish went, and so did her boyfriend Liam [Hemsworth]," the 来源 says of Cyrus. "The group was up until 3 a.m. just dancing up a storm and having fun."
Cyrus seemed quite impressed with Osbourne's planning skills, calling it "the best party ever" on Twitter. "Let's just say there was a unicorn in the lobby!" (An onlooker tells E! News there was a horse with a horn attached to its head inside the soiree.)
Prior to Tuesday's birthday blowout, Osbourne teased that it was "going to be the sickout thing [Miley has] ever seen in her life."
"That was my mission for her, to make her birthday...the best 日 ever."
Osbourne and Cyrus first became 老友记 while shooting the comedy So Undercover. The film has yet to be released.
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