Selena Gomez held yet another birthday celebration to ring in her big 2-1 with family and friends at Revolve Clothing beach house in Malibu on Saturday, July 27, with one famous (and unannounced) face making a late appearance: on-again, off-again boyfriend Justin Bieber.

The "Heartbreaker" singer, 19, arrived at the gypsy-themed house party around 9 p.m., an eyewitness tells Us, dressed down in a black-and-green letterman jacket, dark jeans, with a small present for the birthday girl.

"Justin flew in specifically for the party on a day off from his tour," the source tells Us. "He wasn't dressed in costume, but carried a single red rose in his hand."

Other celebrity guests included Julianne Hough, Nina Dobrev, Derek Hough, Ashley Benson and Jaden Smith, among others. Best friend Taylor Swift was performing at a show and unable to attend.

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"Everybody danced and had a blast, especially Selena, who was surrounded by her friends," an insider tells Us. Gomez's birthday cake was shaped like an elephant on a pillow, with a giant "21" sitting atop the creation, the source tells Us.

Later in the night, Smith helped the Gomez and Bieber sneak out of the house under a blanket and an umbrella, the source tells Us. Gomez and Bieber were holding hands.