Are Lady Gaga & Taylor Kinney Engaged?!

Is Lady Gaga engaged to Taylor Kinney?!

Last night outside of Roseland Ballroom, where Gaga (born Stefani Germanotta) was performing in her New York City residency before the legendary venue closes its doors forever, the "G.U.Y." singer was spotted signing autographs for her beloved Little Monsters ...

... and she was also spotted wearing a diamond ring on her all-important finger.

Kinney surprised Gaga at Roseland Ballroom on Friday, her 28th birthday. The Chicago Fire star smooched his lady love in a photo that she tweeted to fans, captioning the shot, "Another amazing birthday surprise." Aw!

No confirmation has been heard about her ring, which you can peep here -- but considering she and Kinney have been together publicly since 2011 when Kinney co-starred in her "You And I" video, an engagement may not be too far off. After all, they get along famously, and he can put up with and embrace her eccentricities.

Gaga, who claims to be able to orgasm without touch (really), recently gushed on Ellen about her man, calling him a "closet weirdo." "He is extremely strange, actually. And we complement each other's weirdness ... At the end of the day he's my best friend ... and having your lover be your best friend, I mean, it's the best thing ever."

Indeed it is! Congrats (maybe!) to the adorable couple. And dude, imagine that wedding gown.