I seriously can't keep up with these two!  Selena's birthday week wrapped up this week with a huge party last night (Gypsy Theme I might add) and the one and only Bieber showed up to help her celebrate her 21st!

Sources say:

"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."

"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.

Oh yeah and supposedly they LEFT together!

Click her to see all the pics!