TMZ obtained video from Andrea's concert Wednesday night in Italy ... and the legendary singer was doing his thing onstage alongside Johnny, who is playing guitar -- which actually carries some significance.

Johnny and Andrea are performing "En Aranjuez Con Tu Amor" ... a song we're told they originally played together back in 2020, when JD and his good pal Jeff visited Andrea.

The trio recorded their jam session back then, and then Johnny and Andrea played the same song in concert this evening.

In fact, we're told they were able to incorporate the recording of Jeff playing years ago into the performance this evening ... so it's almost as if the three of them are playing together again on stage.

Remember ... Jeff died in 2023 after contracting bacterial meningitis, and Johnny played a tribute concert for his good pal later that same year. Johnny and Beck even toured together in 2022, during the Amber Heard trial.

Johnny's among Andrea's star-studded lineup of guest performers for a series of 3 shows at Teatro del Silenzio in Lajatico, Italy ... Bocelli's hometown in the country's Tuscany region.