Lady Gaga Plays Matchmaker -- Such A Yenta! (VIDEO)

Lady Gaga just gave a couple in England the most AWESOME engagement story ... by helping pull off a surprise marriage proposal during her concert.

Gaga called her friend Jay Lomax and his boyfriend Sean Martins out on stage Tuesday night in Manchester, England. Watch the video (around 1:17) ... Lomax gets down on one knee and pops the question.

Sean tells us he was completely shocked -- and it turns out the whole thing had been plotted for months by Gaga, Jay, and Jay's famous uncle ... photographer (and Gaga friend) Terry Richardson.

Martins says he only got suspicious when Lomax wouldn't let him drink too much at the concert ... and told him to take off his glasses before going out on stage.

Sean says his engagement ring is inscribed with the lyric, "We could belong together" ... from his and Jay's favorite Gaga song, "Artpop."

Martins says there's only one thing that could top the proposal -- having Cher perform at the wedding.