Michael J. Fox can still shred on the guitar ..
. taking the stage alongside Chris Martin and Coldplay -- and playing a mashup "Back to the Future" fans know so well. The actor took the stage at the Glastonbury Music Festival in England Saturday night during the band's headlining set .
.. and, ya gotta watch the video 'cause it's a tear-jerking tribute to the film and TV legend.
The vid kicks off with Chris and the crew jumping into their hit song "Fix You" -- Michael's already onstage, sitting in a wheelchair and holding a guitar on his lap. After a couple minutes, CM heads over to MJF and sings part of the song from his knees so the two are at the same eye level ..
. you can see Michael's hands moving as he fingers and strums the instrument. It's during an interlude in the band's hit song where Martin really highlights Fox though .
.. singing out the lyrics to Chuck Berry 's "Johnny B.
Goode" -- the song sci-fi fans know Fox's Marty McFly played during the climax of 'BTTF.' Michael really comes alive at this part ..
. rocking out from his chair and even throwing a kick out just like he did way back in the 1985 film. The real kicker .
.. Martin credits "Back to the Future" for encouraging Coldplay to start their band -- at which point the crowd breaks into raucous applause.
As you know ...
Fox was diagnosed with Parkinson's way back in the early '90s -- and, he's mainly turned away from acting and toward activism in recent years as the disease has progressed. He gave fans an insid.
