The svelte star has dropped a dress size through the intense workouts on Strictly Come Dancing.
And she says she is enjoying a freedom and confidence she never had in her 30s.
The Italian siren says: "I'm in the best shape now and it's going to get even better. That's my attitude, that the best is yet to come.
"Age isn't written in your documents, it's the age you feel. It's about the spirit and soul of the person.
"I didn't look like this in my 30s, there's always an improvement with age. But we'll see if I'm still saying that when I'm in my 80s."
Today, in the second part of The Sun's exclusive series, Nancy lifts the lid on her beauty and body secrets.
And she reveals that, while she certainly doesn't need to go under the knife, her wrinkle-free forehead is partly thanks to an occasional injection of Botox.
Nancy, who dated former England football manager Sven-Goran Eriksson for ten years, says: "We must always do little things to take care of ourselves which prevent doing major work later on, like facials and even a little Botox when you need it.
"It's something you can do without going too major and you still look like yourself.
"There's nothing wrong with Botox, as long as you have the right doctor and the right measurement. Twice a year is perfect."
Nancy isn't averse to the idea of a little nip and tuck in the future if she feels it's necessary. But she has stern words for cosmetic junkies who get hooked on procedures.
"A lot of those women all look the same," she says. "I support cosmetic surgery at any age if it means a woman will feel happier and more confident, but I don't think it's healthy for women to be obsessed with surgery.
"Any procedure has to suit your personality ? and everything in moderation.
"I would never say never but I hate needles. My hope is that in ten years' time there will be a pill you can take before you go to sleep and you wake up with a facelift."
Born in New York, the eldest of four children to American mother Antonia and Italian father Francesco, Nancy was always a pretty child.
The family moved to Apulia in southern Italy when she was six and she grew up learning the kind of easy glamour typical of European women, from her mum.
It's hard to believe that the confident woman we see on TV, the one that oozes sexual allure, ever felt insecure.
But Nancy says: "Today I'm much more confident than I was ten or even 20 years ago.
"In my 20s I was not confident at all. I know I was attractive because they say I was so sexy with the boys. I never completely believed it.
"It takes time to understand who you are. Your 20s is the most difficult age.
"There have been moments in my life when I have felt insecure or I have had doubts about things. But going through those times makes you stronger."
At 21, Nancy suffered a near fatal accident when a Fiat car hurtled down the wrong side of the road and crashed into her outside her home, throwing her almost 60ft.
She spent a week in a coma and six months in hospital, during which she had to learn to walk again and needed reconstructive surgery on her face.
She says: "When I had my accident I was completely paralysed on one side of my face. The doctors said I couldn't do anything else to my face until I was 40. From the age of 21 to 35, I could still see the scar on my face. Now I can't see the scar, so that's why I look like I'm getting younger and younger."
Nancy puts her lithe figure down to good genes and a sensible attitude to food and exercise.
Her rigorous training with Strictly dance partner Anton du Beke saw her drop from a size eight to a size six.
The workouts are set to continue in the New Year as Nancy is going on the Strictly tour around the UK.
She says: "I did drop a dress size but my body shape also changed and I became more toned.
"Anton told me I could eat all the chocolate I wanted because I would be burning so much energy. I don't believe in diets. Every person needs to learn what are the best foods for you.
"I tend not to eat bread or desserts, but every so often I do. It's not what you do from Christmas Day to Boxing Day but Boxing Day to Christmas.
"Exercise is important but I'm not obsessed by it. Sometimes I'll see my personal trainer two to three times a week. I hate the gym, so instead I power walk and I've got a running machine in the house. I do pilates and yoga too.
"I never use a lift. I'm the kind of person who is burning calories because I'm always moving with my mind and body."
Being in such good shape has led to an approach from Playboy magazine to pose naked. It's something Nancy is considering.
But she says sexiness isn't about what you look like. Nancy, a property lawyer, says: "Sexiness comes from inside. You have to have confidence and be comfortable in your own skin.
"An allure or charisma does make a difference and it's not something you can buy. It is something you can learn though. You have to learn to love yourself.
"There is something in British culture that Brits are afraid to be too confident. It's a less-is-more attitude, but sometimes less is just less. Women can devote more time not just to their appearance, but to their spirituality.
"If you don't look after yourself or like the way you look, how are you going to send a message out there?
"It's not vain, it's being feminine."
Nancy, who is newly single, believes women should embrace their femininity, not hide from it. She says: "There is an art to flirting.
"It's like a wonderful dance of rumba, you shake it, you want it, you're not sure. That is an art that we lost after the great feminist movement. It is important we recover that. It's a new era of women being really flirty and feminine. I can't imagine one day without flirting, it's so boring without flirting."
Nancy is happy to be single for now but says she likes strong, protective men.
She says: "I need a man to make me laugh, to love my space and independence, but at the same time to take care of me because that's a man's role."
When it comes to style, the woman who once famously strode into Downing Street in a plunging red catsuit believes fashion is also important in creating the right image.
"I do like to always be glamourous," she says. "I think accessories and details are important. People say to me, 'You're so coordinated,' but that's me, it's natural.
"Fashion is how we express ourselves, whether that's being glamourous and sexy, or fun and playful.
"I always like to wear something that reflects my state of mind."
All the same, Nancy insists she is just like the rest of us and will even slip on a tracksuit in the house.
