Video footage obtained by TMZ shows 50 urging the crowd to "turn it up even more" with a massive digital box descending onstage along to the beat of Ed's "Shape Of You."

Rap fans look perplexed at the unexpected voyage into pop as the British singer's vocals are heard live in the distance -- and when 50 instructs the audience to "put their hands up," the box lifts to unveil Ed himself.

Cheers erupted from delighted concertgoers ... quickly whipping out their phones for evidence of the dynamic music collab onstage.

This isn't the first time 50 has stunned fans with a plus one on stage ... bringing out the likes of Busta Rhymes and Eminem.