Minnelli is in London with fiancé David Gest
The Academy Award-winner is in London to promote a series of European concerts, together with producer David Gest, who will become her fourth husband in March.
Singer Michael Jackson will be the best man at the wedding and Dame Elizabeth Taylor is the matron of honour.
Minnelli, 55, has shed 90lbs after battling back from encephalitis.
"David inspired me. I lost a lot of weight and it helped me because I have a bad back - the thinner I stay the better I feel," she said.
"I'm a thoroughbred, literally thorough bred and it's an inner strength that my parents gave me, especially my mother," she added.
"A year ago, this time, she could not walk and she could not talk. They said she'd never sing again and she was in a wheelchair," Gest said.
"She has lost 90 pounds (40 kilograms)- how many of you could get through that and a year later be standing looking as fabulous as this woman?" he added.
"That's remarkable, she's a remarkable human being."
The couple first met at the home of Frank Sinatra more than 15 years ago.
Mr Gest said: "It was just 'Hello Ms Minnelli, hello Mr Gest', very simple, but then we didn't see each other again for another 15 years."
Dinner
They teamed up after Mr Gest worked as producer on Jackson's comeback concert last September, where Minnelli made her first appearance after her illness.
"When we met the first time at her house, really met, we kind of knew what was going to happen. We went out to dinner and that was it," said Mr Gest.
Minnelli was born in March 1946 to screen legend Judy Garland.
It was in 1972 that she emerged from the shadow of her mother with a show-stopping performance in the hit musical Cabaret, a role which earned her an Academy Award.
The singer kicks off a set of European shows with five nights at London's Royal Albert Hall starting on 2 April.
Minnelli said her new stage show would be made up of classics from Cabaret, as well as more contemporary R'n'B tunes with a few new compositions.
"It's a whole new gig. You'll be surprised."