’24’ star Sarah Wynter’s dad was a shotgun killer!

Respected physician Dr. Stuart Wynter gunned down his second wife and his 4-year-old daughter — Sarah’s half-sister — in his home, then turned the gun on himself and committed suicide, police say.

The 30-year-old actress, who plays Kate Warner on the hit TV series, refuses to discuss the grisly secret from her past. But Sarah’s mother Helen believes her decision to divorce Dr. Wynter six years earlier saved the lives of Sarah and Sarah’s younger brother Brendan, as well as saving her own life, a friend said.

Dr. Wynter, 38, blew away his wife Rakentati and his daughter Binatia with a 12-gauge shotgun on March 11, 1984, at their home in tiny Heathcote, Australia.

“DOCTOR IN KILL RAMPAGE,” screamed a headline in the local paper.

Rakentati, 28, was a beautiful South Seas islander who had fallen in love with the doctor while he was working in the Gilbert Islands. Dr. Wynter married his new love in 1979 — just a year after Sarah’s mother had walked out on him, taking Sarah and Brendan with her.

Two days after the murder-suicide, a fellow doctor called police when Dr. Wynter failed to show up for work at his family practice near his home.

Cops found Binatia’s tiny body slumped in an open closet — having been hurled across the room by a shotgun blast.

The doctor was found draped over Rakentati’s seminude corpse, with the shotgun by his side. The victims each died from a single blast to the head, police said.

Police in the close-knit community were stunned. Sgt. Fred Hobley recalled that Dr. Wynter had once saved his life by reviving him after a heart attack.

“He was my doctor — but as well as being my doctor, he was like one of the family,” Hobley said. “Everyone was completely shocked.”

To most townspeople, Dr. Wynter had appeared happy.

“He wasn’t a playboy or anything,” said local gas station owner Mark Fasso. “He was a really quiet guy.”

But behind closed doors, furious arguments raged, a colleague revealed.

Dr. James Casey said when he visited the Wynter home hours before the murders, Dr. Wynter told him of a fight he’d had with Rakentati, during which she’d slashed a mattress and bedcovers with scissors. He said he saw Dr. Wynter take a tranquilizer and heard Rakentati call from a bedroom that she couldn’t be helped because she was crazy.

Sarah was 11 at the time of the murders. A newspaper death notice appeared soon afterward, saying of Dr. Wynter: “Loved father of Sarah and Brendan Wynter . . . in God’s care.”