Marty McFly & Doc Brown -- Back to the Back to the Future

Fire up the flux capacitor -- It's been nearly 30 years since the first "Back to the Future" movie hit the big screen ... but Michael J. Fox and co-star Christopher Lloyd are still going strong.

Lloyd and Fox re-joined forces today in NYC while on the set of "The Michael J. Fox Show." Lloyd is set to appear in a cameo role ... but nothing will ever rival his timeless work as Dr. Emmett Brown.

FYI, Lloyd is now 75 years old.

GREAT SCOTT!!!