Kitty Spencer weighs in

Far from being identified with her pencil-thin model mother, or Princess Diana, the 19-year-old is often teased about being overweight. Munching on a greasy toasted cheese sandwich and large plate of chips, she says: "I'm called chunky' and big thighs' but I'm not going to do anything about it, or worry about my weight."

The eldest daughter of Earl Spencer, who splits the year between London and Cape Town, went on: "I know I'm not a beanpole, but so what? There's a gym in the house, literally next door to my bedroom. I've walked past and looked in but I've never been inside. I don't enjoy exercise, so I don't do it. Many girls my age have a weight obsession but I haven't — it's too boring to bother trying to keep thin, life's too short."

At 5ft 8in Kitty isn't quite as tall as Princess Diana. And unlike the princess, she doesn't even weigh herself, revealing that her mother won't countenance scales at home. "My mum says it's unhealthy having scales in the house — they're banned," she said. "On top of that, I always find, especially when I'm studying hard, that I don't crave healthy food, I just want to eat junk. I love instant noodles with grated cheese on top. I love pizza and pasta."

Kitty has learned to laugh off remarks about her weight and is undaunted by the fact that she is engaged to a model and pin-up, South African soccer player Larry Cohen.

"I get criticised about my weight quite a lot," she admits, "it doesn't upset me because I just think it's unhealthy. My friends told me that someone said I had fat thighs on some website and I should go and look at the comments, but I don't want to. I just think if I was the other way, skinny, then people would say I was too skinny, so you can't win, and as long as I'm happy and doing what I want, I don't let it affect me."

Kitty is at pains to prove herself as a serious, intelligent woman who studies hard — she is reading psychology, politics and English literature at Cape Town University — and the last thing she would want to be known as is a society girl. "I'm sick of being compared to other people and I just want to achieve stuff in my own right, for my self-worth and self-respect. I don't just want a BA, I want a triple major, then I don't care how people judge me because I know how hard I've worked. I've always worked really hard in school, I was a proper geek. I used to wake at five in the morning and study."

Kitty is close to her father and has seen him through three relationships: with her mother, his next marriage to Caroline Freud, and now his new fiancée Lady (Bianca) Eliot, widow of Lord Jago Eliot and a mother of three. The Earl phones his daughter daily and never goes longer than a couple of months without seeing her. They holiday together four times a year, and spend the long English summers at the Spencer family estate in Althorp, the family seat that Kitty's younger brother Louis, will one day inherit.

"I have my room at Althorp, which is full of childhood stuff. I love it. It's got pink walls, all my teddy bears from when I was little, and pictures of me and my parents when I was little and pictures of my christening. It's like going back in time.

"I don't think there's anything from Diana in my room but the museum's out in the stable block, so all her stuff is there. We go to Althorp four times a year, for school holidays. It's beautiful. You're in the countryside so it's the perfect place to relax. All our family comes to stay." For a young girl whose mother has admitted contemplating suicide and attends recovery meetings to prevent her falling back into drug abuse; whose aunt died in a shocking car accident; and whose father is embarking on his third marriage after an extremely messy public divorce from Kitty's mother when she was seven, Kitty appears remarkably well-adjusted and of sunny disposition.

"I'm sure it affected me when my parents got divorced but I was so young," says Kitty. "And when I think about it now, I know I wouldn't have my half-siblings, Samuel, Ned, Lauren — so many wonderful people would not have been brought into my life were it not for all the divorces and second families."

Just months before her parents parted, Kitty's father had given "that speech" at Princess Diana's funeral. "I'm proud of him for saying that," says Kitty. "When anyone stands up for what they believe in, it is admirable — and, let's not forget, it took a lot of courage."

She believes that that time left an indelible marked on her psyche. "I think I've inherited my father's strong, outspoken streak. I can definitely stand up for myself."