Mark Harmon — Shocking Final Days Of ‘NCIS’ Star’s Sister

Mark Harmon plays a good guy on the hit crime drama "NCIS," but angry insiders are blasting the TV investigator as a cold-hearted creep with a history of chasing skirts!

A family feud had sources blasting Mark (here beside "NCIS" costar Pauley Perrette) as far from the “fair-minded hero he plays on TV,” said a source. “Mark can be a total jerk!”

His dirt-poor sister Kristin Nelson, 72, passed away on April 27 from a sudden heart attack — barely a year after being released from a Santa Fe hospital. At the time, reported sources, Mark refused to visit her or pick up the phone. “Kristin is nearly destitute,” an angry insider said at the time.

“She got a small inheritance from her mother who died in 2012,” continued the source, “but that money’s virtually gone now.” The source added that Mark — who's been reported to have feuded with "NCIS" co-stars — is “worth millions. He won’t kick in a penny to help her out!”

Sources said the star’s bitterness stemmed from the late 1980s, when he tried to take away Kristin’s kid using the power of his pocketbook, celebrity and high-powered lawyers — only to mysteriously drop his lawsuit under suspicious circumstances.

In 1987, the former "St. Elsewhere" star and his "Mork & Mindy" wife Pam Dawber hauled widow Kristin, whose husband was pop star Ricky Nelson, into court on claims she was doing drugs around her son Sam. Kristin vehemently denied it under oath.

She still might have lost her child, but Mark shockingly dropped the suit at the 11th hour just before Pam, who was secretly four-weeks pregnant with their first child, was to be grilled about her own drug use. Pam insisted she didn’t do drugs. At the time, Kristin’s lawyer claimed Mark’s decision to drop the case was “unconditional surrender.”

Mark also knows that his family has health issues. In 1990, his dad Tom (right, with Mark and his mom Elyse Knox in 1986), a Heisman-Trophy winner and World War II hero-turned-sportscaster, suffered a massive heart attack after winning a golf tournament at Bel-Air Country Club. He was rushed to UCLA Medical Center, where he died.

“Losing his father in an instant like that, when he seemed the picture of health, still rattles him to this day,” said our insider. “For a time in 2015, at seemingly the height of his fame on 'NCIS,' he seriously mulled calling it quits to be with Pam and their two kids.”

But the family man still has a wild womanizing past. As a young actor, he plunged into sizzling affairs with a bevy of Tinseltown beauties. His list of conquests includes 'Knots Landing' starlet Donna Mills, singer Karen Carpenter and "Flamingo Road" co-star Cristina Raines (right)!

At the time, Mills described Mark as catnip to women, gushing: “Forget Mel Gibson. Whenever I see Mark, I think to myself, ‘Your place or mine?’ ” Even Mark confessed while playing rakish Dr. Robert Caldwell on "St. Elsewhere."

“Women would come up to me and show me their breasts and ask for my opinion." Mark said at the time. "And I gave it to them!”