Toni McHugh has spoken of her terror on realising that the man she once loved, Gerard Baden-Clay, was a philanderer and a killer.

Toni McHugh once longed to be Mrs Baden-Clay and she believed her longtime lover would one day make that dream a reality.

Now, Queensland’s most notorious mistress has spoken of her terror on knowing the former real estate agent Gerard Baden-Clay was a killer.

Baden-Clay was this week found guilty of murdering his wife, former beauty queen Allison, and sentenced to life in prison.

He’ll be eligible for release in 15 years but has already launched an appeal against his conviction.

Crucial to the court case was Ms McHugh, who turned star prosecution witness and told the jury of her on-off lover’s double life.

“I don’t like to use that word `unconditional’ anymore, but I did love him unconditionally,” Ms McHugh said on Sunday, in a tell-all interview with the Nine Network.

“I was very forgiving. Too forgiving.”

Allison’s badly decomposed body was found lying on a creek bed 13km away from the family home in the affluent Brisbane suburb of Brookfield on April 30, 2012.

The grim discovery came 10 days after Baden-Clay reported her missing, and four years after he first embarked on an affair with an employee, Ms McHugh.

During his 21-day trial Baden-Clay made much of Allison’s struggle with depression and tearfully admitted to multiple infidelities.

He said he hadn’t been intimate with his wife for years and “just wanted sex” from other women.

Ms McHugh said she still felt an element of disbelief about her former lover’s dark side, but refused to believe her long-running liaison with Baden-Clay led to Allison’s murder.

“I’ll never understand how it could have happened. I don’t believe that he murdered her for me,” she said.

“Why I say he did not kill her to be with me was that I loved him already. He didn’t need to. He already had me … He killed for himself.”

She said she fell for her boss because she admired him, believed in his integrity, felt an attraction and love blossomed.

Baden-Clay promised he would marry his mistress and Ms McHugh said she was impatient for him to leave his wife.

Now, she wants nothing to do with him.

“I want this man to never, ever, ever enter my life ever again,” a tearful Ms McHugh said.

“There is a part of me that is genuinely fearful that I have been involved with a man that is not who he says he is. And that worries me. That terrifies me.”

She said she was “devastated” when she found out Allison was missing and had never wanted to hurt her.

“My first response was, did you argue? He said no. I felt terrible,” she said.

But she accepted that she played a role in Allison’s internal heartbreak.

“But what I also know is that if it wasn’t me, it would have been someone else. He would have had affairs with other women,” she said.