In a free-wheeling interview to the Daily Mail, Kath says she often felt bitterly humiliated over her husband's betrayal in the year 2000, and after enduring six months of suspicion, during which she was convinced about his two-timing ways, she served him an ultimatum to behave or get out.
"If you don't want to be with me any more, there's no point in going on," she told Ian.
Describing him as being moody and short-tempered during that time, Kath told the paper that it was obvious he couldn't bear to be near her, and she acquired proof when she accidentally overheard him whispering goodbye to his lover on the telephone as she passed his study during a lull in Christmas festivities at their home in North Yorkshire in 2000.
After almost 25 tempestuous years of marriage to "Beefy" - England 's greatest cricket all-rounder, leading wicket-taker and TV commentator, she said: "I wasn't prepared to let Ian treat me like that."
"I knew he was having an affair because of his whole attitude towards me. He was very short and didn't want to be around me," says Kath, speaking for the first time about her husband's affair.
"Everyone had noticed. Even our daughter Becky, who's a real Daddy's girl, said: "I don't know why he's bothering to come home because he's not very nice to you. "I'd confided in a few people about my fears, but our son Liam had said: 'No way Mum, Dad would never do that to you," she added.
She also said that she talked to her mother - Jan - about the decision she was about to take, and at the beginning of January 2001, just three weeks before their silver wedding anniversary, she confronted Ian, and he admitted everything.
"Sorry has never been a word in Ian's vocabulary - I'd be surprised if he'd uttered it once during our marriage - but he immediately apologised," says Kath.
"He told me he didn't want to break up and had been a complete fool. He simply caved in and promised to do whatever I wanted to save our marriage, which surprised me," she added
Ian ended his two-year affair with 31-year-old Australian waitress Kylie Verrells, a single mother he'd met on New Year's Eve 1998 in Sydney, where he was commentating on the Ashes.
And Verrells sold her story for a reported 40,000 pounds, revealing how Botham flew her round the world to be with him, sent smutty e-mails, set up a public speaking company with her and, giving her a sapphire and diamond engagement ring, and promised to leave Kath.
Ian issued a grovelling public apology to his family for the embarrassment and distress he'd caused.
Ian was was knighted last month
The Bothams' children Liam, now 29, Sarah, now 28, and Becky, now 21, were completely shaken by his betrayal.
That, however, was almost seven years ago and much has since changed. For a start, Kath, trim and glowing at 52, is positively radiant and says, amazingly, she has never been happier with Ian.
Last year the Bothams celebrated their 30th wedding anniversary and their 50th birthdays with a safari holiday in Africa. Ian's gift - a beautiful Tiffany diamond eternity ring - is now twinkling on Kath's slender finger.
The icing on the cake came last month when Ian Botham OBE became Sir Ian Botham. Kath is now Lady Botham.
She is proud that such an honour has been bestowed on Ian, 51, for his tireless charity work, during which he's raised over 10 million pounds for the Teenage Cancer Trust and Leukemia Research.
Kath told the paper that it was she who planned almost all of his 11 long-distance sponsored walks, covering more than 5,000 miles, and she was the first person on a long roll call of people Sir Ian paid tribute to.
"To be honest, Ian is more proud of his charity work than his cricketing career. He says he won't stop until there is a cure for leukemia," says Kath.
The minute we found out about the knighthood, I told him: 'You deserve it. It still hasn't sunk in, but it won't change us. Family is more important than titles. What really matters is that I have my husband back, my children have their father back and their children have Grandad back."
"He still annoys me, we still argue, but we love each other too. The affair will never go away, it will always be there, but I have learned to deal with it. Ian's behaviour since has been hugely reassuring and he's worked really hard with the children to repair the damage," she said.