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!.