TMZ has learned Stone came to the rescue of a forgetful taxi passenger named Mark this weekend -- after the guy left his cell phone in a New York City cab.
Mark tells TMZ Stone found his phone in the cab, got in touch with him, and set up a meeting at JFK airport -- but Stone never revealed his identity.
Mark says despite the fact he was 30 minutes late -- jeopardizing Stone catching his own flight -- the chef was still there waiting with "a smile on his face."
Mark -- a big "Apprentice" fan -- says it took him a second to recognize Stone ... and when he asked Stone if he was "the guy from TV" he just said, "Gotta catch my flight" and then took off.
Curtis ... You're hired.