The shocking instant DEBBIE REYNOLDS  knew her marriage to crooner EDDIE FISHER was over —  She caught him in bed with her BFF ELIZABETH TAYLOR!

 Hollywood icon, Debbie, now 82, recalled in an interview how her storybook marriage to Fisher, who rivaled Frank Sinatra in popularity, was shattered with one phone call.

Eddie may have introduced the All-American MGM starlet Debbie as "his princess" onstage but behind closed doors, he sang a different tune.

One lonely night with Eddie away on tour, Debbie called BFF Liz for a chat.

To her horror, Eddie picked up!

"Suddenly, a lot of things clicked into place," Debbie recalled.

"'I could hear her voice asking him who was calling – they were obviously in bed together.

"I yelled at him, 'Roll over, darling and let me speak to Elizabeth'.

Fisher then slammed the receiver down, rushing home for a showdown with wife Debbie with the chilling words she still remembers:  'I'm sorry. Elizabeth and I are in love and I want a divorce.'

Debbie snapped, "If you marry her, she will throw you out within 18 months!"

"And Elizabeth did get rid of him, just as I had warned, when she met Richard Burton on the set of Cleopatra," Debbie said.

Ironically, Eddie had been best man at Liz's wedding to showman Mike Todd, who died in a plane crash, and Debbie a bridesmaid.

'I was the last to find out about the affair," Debbie said.

"Although I didn't want to find out the truth, I had to face up to it. Even so, it was a great shock to find them together. It left me shattered."