Demi Lovato Birthday: Miley Cyrus, Kim Kardashian Among Celebs to Tweet Happy Birthday Wishes

Demi Lovato, the popular Disney star turned "X Factor" judge, celebrates her 20^th birthday on Monday. Along with a cute Twitpic posted by Kim Kardashian of the two celebs blowing kisses at the camera, some other big names also took to Twitter to wish the "Give Your Heart a Break" singer a very happy birthday:

@KimKardashian: "Happy 20th Birthday DemDem!!!! I love you @ddlovato."

@mileycyrus: "@ddlovato happy birthday beautiful," she wrote. "I'm sending you lots if x's not wasting time on o's =] have the best day everrrr xxxx."

@TheXFactorUSA: "we were thinking of getting you a pig named Simon for your birthday... but we figured one Simon is enough ;)"

@NiallOfficial (Niall Horan of One Direction): "@ddlovato happy birthday honey! Have a lovely day! See ya soon."

@rogergzz (Roger Gonzalez of Disney Channel): "Happy birthday princess @ddlovato LOVE U!"

@SimonCowell: "Happy Birthday Brat (@ddlovato) lots of love. Simon."