Jill Thorne said it sent the popular player and TV commentator into a spiral of depression and debt from which he never recovered.
She added: “It was the start of the end for him.”
Willie – who died from leukaemia in June – was axed as a World Championships commentator at the Crucible in 2017 after more than 30 years.
It caused an outcry amongst the sport’s top stars, including seven-time world champion Stephen Hendry. Former Miss GB Jill told how Willie, 66, was never given a reason for being dropped.
He had battled depression and a gambling addiction for years, and was declared bankrupt after losing £1million. But Jill said it was his BBC axing which “destroyed Willie”.
She added: “He loved the job and was loved by all the ex-pros and fans.
“I could have accepted it if they gave Willie a reason but they didn’t, just calling it an ‘editorial decision’.
“He tried to put a brave face on it, but all the old demons he had been battling came flooding back and his confidence went through the floor. From that moment on I really lost him. It was the start of the end for him.”
Jill went on: “I was with him in the car when he got the call. It was on loudspeaker and I heard every word. They didn’t give a reason, they just said his contract wasn’t being renewed.
“The colour drained from his face and he had to pull over he was so upset.
“After that he just went into a spiral of depression. It was like he was grieving for the job. At the time it was his main income, too.
“After that he was just going downhill, he had terrible mood swings, it was like he stopped caring about himself.”
Jill said they moved to Spain to try for a fresh start. But his financial woes continued and she made the heartbreaking decision to leave him after 24 years together.
Willie’s health deteriorated but Jill said they remained pals until his death, adding: “It’s a great shame for him that he went downhill so quickly. We were friends at the end, we spoke every day.
“Now the World Championships are on I can’t bring myself to watch it because of what the BBC did to Willie.”
Jill plans to organise snooker and golf tournaments to raise cash in his memory for the 20-20 Voice Cancer charity, after she took over from Willie as patron.