Christina Aguilera's "mystery man" for her evening out at SoHo in Los Angeles Friday night was Matthew D. Rutler, a set assistant from the production of Burlesque, RadarOnline.com has learned.

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Christina and Rutler doubled-dated with her friends Nicole Richie and Joel Madden, and they did their best to keep Matthew hidden. Some websites even incorrectly reported that it was Benji Madden in the back seat with Christina!

The tall, good-looking Rutler is also a guitarist for the Nate Mott Band, according to his imdb listing.

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He and Christina also reportedly went out together on Halloween.

Aguilera shocked fans last month when she announced she and husband Jordan Bratman had separated after five years of marriage. They have a son, Max.

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Since then, Christina has partied in Honolulu, performed at the Justin Timberlake Friends benefit concert, and hung out with her pals in L.A., New York and Miami.

Rutler is just back from Hawaii where he worked on Just Go With It with Jennifer Aniston and Nicole Kidman.

Burlesque, the movie where Christina and Rutler met, opens November 24.

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