Rushing home to stop hubby CLARK GABLE from bedding LANA TURNER, screen beauty CAROLE LOMBARD won a coin toss – and lost her life in a fiery plane crash!

That’s one of the shocking secrets surrounding the screen legend’s tragic death unveiled in the blockbuster new book, “Fireball: Carole Lombard & the Mystery of Flight  3”

Worried her husband Clark Gable was having an affair with sexy starlet Lana Turner, the "To Be or Not to be" star Lombard insisted on hopping on a military plane instead of taking a train back home to L.A. from a 1942 World War II bond-raising tour.

But her mother Elizabeth Peters and Gable’s publicist Otto Winkler had a fear of flying and balked, so they flipped a coin.  Lombard won and the three boarded a plane doomed to a fiery Jan. 16, 1942, crash, killing all on board.

“If she hadn’t felt so threatened by Turner that she needed to rush home to Gable at breakneck speed on a plane instead of a train, she would have lived,” writes author Robert Matzen.

Ironically, federal authorities had forbidden stars like Lombard from flying on tours “because of the vulnerability of airplanes,” Matzen writes.

AND the "Nothing Sacred" star had promised her entourage they’d travel only by train.

But by the time they’d reached their final tour stop in Indianapolis, Lombard was frazzled by the thought her hubby, who stayed home to film “Somewhere I’ll Find You”, was having an affair with co-star Turner.

While Gable had a slew of flings, writes Matzen, “Carole found Lana too young, too blonde, and way too much on the make.”

After the coin flip, Lady Luck tried to intervene again when all civilians were ordered to give up their seats to Army Air Corps personnel, but Lombard refused.

The actress, 33, Peters and Winkler were aboard the TWA fight when it slammed into the Potosi Mountain outside Las Vegas and exploded.

Gable, then 40, was devastated.

He wed twice more, but died Nov. 16, 1960, still haunted by Lombard’s loss.

“The capacity for happiness had left him,” the book says.