If it’s up to DAVID McCALLUM, don’t expect a “Man From U.N.C.L.E.” reunion on “NCIS” anytime soon!

Due to bitter feelings that won’t fade away, David McCallum – medical examiner Donald “Ducky” Mallard on the top-rated CBS series – is dead-set against reuniting with his “U.N.C.L.E.” co-star Robert Vaughn, sources say.

“Robert would love to do a guest-starring role on ‘NCIS.’ He’s said as much over the years, but David doesn’t want him on the show,” said a source close to the production.

That’s because McCallum – who played a Russian agent on the ’60s spy hit – is determined to keep his “U.N.C.L.E.” career separate from “NCIS,” said the source.

When a reporter from a French website asked McCallum if there was a chance his 79-year-old pal Vaughn – star of the long-running British TV series “Hustle” – might be on “NCIS,” he shocked many when he replied: “I hope not.”

McCallum, 78, pointed out that while it would be easy to put together, he felt it would be the wrong move.

“David maintained that it was ‘important to separate these two worlds,’” said the insider. “He said, ‘Robert Vaughn has his series, I have mine. Enough!’

“The truth is that David feels ‘NCIS’ is his show and he doesn’t want Robert tromping on his turf. He had to share the spot­light with Robert on ‘U.N.C.L.E.’ and he felt he often got the short end of the stick. He doesn’t want to dredge that up again.”

Despite that, “NCIS” has poked fun at McCallum’s past as the dreamy-looking spy on “U.N.C.L.E.”

When “NCIS” Special Agent Jethro Gibbs – played by Mark Harmon – was once asked what Ducky looked like as a young man, Gibbs replied: “Illya Kuryakin.”

Meanwhile, diehard “NCIS” fans continue to clamor for the “U.N.C.L.E.” reunion.

But the source said: “Unless David changes his mind, it won’t happen.”