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Queen B held court at Les Deux last night -- kicking off the evening at 10:15, just after the club opened, and lasting until 1:30 am!

Brit arrived with Alli and and a mystery guy who chauffeured them in a black BMW -- the gang went straight to the best VIP table in the house. An X17 source inside the club said Britney seemed to be in a relatively good mood and she appeared most interested in listening to the music and dancing in her seat.

Not too long after the Dynamic Duo arrived, Avril Lavigne showed up and joined them at the table and stayed with them until "the bitter end," our source says.

Just after the clock struck 1:30, the whole group left -- Britney and Avril separately, and headed home.

Wild nights, y'all!