Dan Blocker was one of the true fan-favourites on retro television.

The actor played "Hoss Cartwright" on Bonanza for the show's first 13 seasons. "Hoss" was the charming gentle giant who kept fans tuning in alongside stars like Michael Landon and Lorne Greene. But, sadly, tragedy struck in 1972.

Bonanza: How "Hoss" actor Dan Blocker died

Bonanza had just aired its season 13 finale in April of 1972. One month later, the show and its fans were dealt a tragic blow: Dan Blocker had died suddenly at the age of just 43.

Blocker's death came on May 13, 1972, after he'd gone in for gall bladder surgery. Several days after the procedure, he awoke with difficulty breathing and returned to the hospital. He "developed a blood clot in his lung, and died," reported The Austin Chronicle.

Dan Blocker's cause of death: Pulmonary embolus

The blood clot, also known as a pulmonary embolus, was listed as Blocker's cause of death, according to The New York Times.

He died at the Daniel Freeman Hospital in Inglewood, California, leaving behind four children, his wife Dolphia, and a legion of heartbroken Bonanza fans.

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Bonanza actor Dan Blocker's cause of death: Pulmonary embolus

There was uncertainty on how Bonanza would go on without Blocker, who was one of the three main stars since season 1. Ultimately, it only aired one more season, as ratings declined perhaps in part due to Blocker's absence.

Bonanza didn't explicitly say that "Hoss" died on the show, but the season 14 episode "Forever" implied the character had passed away — just as Blocker had.

You can also click here to see which Bonanza actors are still living today.