Jen Helps John Jumpstart His Birthday

Today may be John Mayer's actual 31st birthday, but Jennifer Aniston helped the singer get a head start on his special day by going out to dinner the night before!

Jen marked the occasion Wednesday night by attending John's birthday bash at L.A.’s members’ only cigar club, Grand Havana Room.

Around 1:30 a.m., the reunited couple were spotted leaving the club together.

“Jen and John were seen in the back seat of her grey Suburban security car, driving out of the underground parking structure,” an eyewitness tells OK!.

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This is only the latest date in the reignited relationship between John and Jen. After spending most of 2008 by each other's side, the couple split suddenly in August, only to be spotted out together this week in both NYC and L.A.

"Jennifer Aniston is the smartest, most sophisticated person I think I've ever met," John told OK! shortly after the two parted ways. "She's one of the most lovely people I've ever met in my life."