She explains that despite attending rehab seven times and a mental institution twice, it was only when her mum Sharon Osbourne was diagnosed with cancer that she decided to change.
Speaking to Cosmopolitan magazine, the TV presenter said: "I was faced with the choice of a career or spending what could have been the last days of my mother's life with her… I became my mum’s nurse 24/7. I thought I was going to lose her – it was awful."
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She added that despite all the help she got, she had to choose to transform herself. "What I've learnt is that no amount of therapy or medication is going to work unless you want it to. Until you want to be a good person, you will never be one."
Kelly, who got engaged to vegan chef Matthew Mosshart in July after meeting at Kate Moss' wedding in July 2011, also spoke out about falling head over heels in love.
"I'm so lucky to have somebody as special as Matthew. I tend not to talk about relationships, because everything else is so out there and the only thing that is mine is my fiancé.
"The only thing I’ll say is that you will never learn what love is on any level until you let someone love you the way you deserve to be loved. I want to have kids – a boy and a girl… I’d like to live in England when I do, as I will not have a baby call me 'Mom'."
The 28-year-old, who is now a presenter of E!'s hit show Fashion Police, is clearly in a good place in her life. Speaking about the pressure of being in the spotlight since she was born, and the criticism that she has received over the years for her appearance and her weight, she had wise words to share.
"What's been great is overcoming that… I'm not perfect, but I don't want to be the prettiest in the room.
It's about realising that, no matter how hard you try, you will only ever be yourself."