If you're rich, famous and today's coincidentally your birthday, what do you do?

Celebrate it like Miley Cyrus does, that's what.

Savoring her last year as a teen (she's now 19), the Disney star mixed the adult bash at the Hollywood Roosevelt hotel with something a bit peculiar - unicorns.

While the party was on-going, a unicorn was seen walking around outside the venue. Obviously, it isn't the mythological creature brought to life, but only a horse with a horn carefully attached to its head.

Cyrus' 'So Undercover' co-star, Kelly Osbourne, was the one who did all the planning for the party, promising all sorts of "madness and craziness".

"It's intimate, but it's going to be the sickest thing she's ever seen in her life," the 'Fashion Police' host shares to E!.

She wasn't kidding.

Come to think of it, it is kind of sweet for Osbourne to go through all this - she's been on to this for days - since Cyrus was the one who helped with her own birthday last month at the Little Door restaurant in LA.

"Although I see her on the same level mentally as me, I also realize that Miley's 19 and she deserves to still have fun," Ozzy's daughter tells of her gal pal.

"Because that girl has so much pressure on her and has worked her ass off her entire life that I think a lot of the time people forget that she deserves to have fun too. So that was my mission for her, to make her birthday...the best day ever." added Osbourne.

True enough, the 'Hannah Montana' star seemed to had a blast together with her celebrity friends.

Her boyfriend, Liam Hemsworth, mother, Tish Cyrus, and sister, Brandi, were also present on the private rendezvous held inside the Beacher's Madhouse Club, which Osbourne rented.

"The group was up until 3 A.M., just dancing up a storm and having fun," a source tells MSN.

Not forgetting to give credit where its due, Cyrus thanked her publicly on Twitter.

"Can't thank @MissKellyO for the best partyyyy ever! =]]]] i loveeeee you! Let's just say there was a unicorn in the lobby!," the star tweeted.

Thank goodness it isn't a giant salvia, though.

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