#TBT: See 'The Voice' Judges Gwen Stefani and Christina Aguilera Party in 2005!

#TBT: See 'The Voice' Judges Gwen Stefani and Christina Aguilera Party in 2005!
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Who knew? Christina Aguilera and her soon-to-be replacement on The VoiceGwen Stefani, go way back! 

Earlier this week, Aguilera, 33, revealed that Stefani, 44, would be replacing her as a judge on the singing competition. The No Doubt singer responded by congratulating Aguilera on her pregnancy!

"@xtina congrats on yr baby bunny Apollo & i cant wait to hang out w all the crazies #thevoice #surroundedbyboys gx," she wrote, referring to her baby boy, Apollo, who was born Feb. 28.

Stefani also shared a priceless throwback picture with the "Beautiful" singer. In the pic from 2005, the two blondes are spotted partying at the Vanity Fair Oscar Party with Pamela Anderson.

Crazy -- we never knew these two were amigas