He was the strikingly handsome and slightly broody actor from hit TV dramas St. Elsewhere and Flamingo Road; she was the adorable and sweet star of beloved sitcoms Mork &Mindy and My Sister Sam.

When Mark Harmon and Pam Dawber met in the 1980s, they were a match made in Hollywood heaven.

But unlike most famous couples, the duo has stayed together for more than three decades.

And they’ve managed to do so without making headlines over cheating scandals, vicious fights or nasty divorce rumors.

But that doesn’t mean Mark and Pam, both 67, haven’t had their fair share of issues behind closed doors. An insider tells Star the fiercely private pair have seen some dark days. “They’ve had a lot of highs,” reveals the source of the couple, who wed in March 1987 and welcomed sons Sean, 31, and Ty, 26, soon after. “But there have also been some lows.” The insider says a bitter family feud involving Mark’s now-late sister “almost pushed Mark and Pam to the brink,” and adds that Mark’s high-pressure gig as the star and an executive producer of the hit CBS series NCIS has also caused major tension at home. “Their marriage has been carefully guarded,” says the source, “but it hasn’t always been wedded bliss.”