Not letting her 21st birthday fall by the wayside is Selena Gomez. Though the singer celebrated her milestone a week ago, Selena kept the party going this weekend and the biggest present she got was a surprise appearance by on-again off-again boyfriend Justin Bieber. Right around midnight a source tells People Magazine that Justin showed up in his leopard print Audi dressed casually and carrying a single rose. When the birthday girl saw him, she started crying and the two snuck off together. What do you think, tears of joy or sadness?