Anne Glenconner was born Lady Anne Coke in 1932. The eldest daughter of the 5th Earl of Leicester, she grew up at Holkham Hall in Norfolk and was a childhood friend of the late Queen and Princess Margaret and a maid of honour at the Queen’s coronation. She married Colin Tennant, later Lord Glenconner and the owner of Mustique, an island in the West Indies, in 1956. They had five children together, of whom three survive. Her son Charlie, a former heroin addict, died of hepatitis in 1996. Her son Henry died of Aids in 1990. She was appointed lady in waiting to Princess Margaret in 1971. Her first book, a memoir called Lady in Waiting, was published in 2019 and became a surprise hit. Now she has written another, Whatever Next?, in which she reveals that during her marriage she was a victim of domestic violence. Why did you decide to write a second memoir? There was a great deal more that I wanted to say. But the publication of Lady in Waiting made me braver. It is extraordinary to become a bestselling author at 87, your book translated into 12 languages. You were born into another world. Did the cooks at Holkham really gather up the shed velvet from deers’ antlers, fry it and serve it on toast? Yes, they did and if the footman carried raw eggs in a bain-marie from the kitchen to the nursery, it was so far, they were boiled on arrival. The world has changed immeasurably. I think anyone who lived through the war was marked for ever by it. We went through such a lot. I do find it a bit strange what people complain about nowadays. But isn’t stoicism a double-edged sword? As you admit in your book, life might have been better for you and your children if you’d talked more. Yes, but thanks to this book, I’ve had the most wonderful conversations with them. We’ve been able to talk about what Colin, their father, did to them in great detail and I’ve been able to say: “Oh, darlings.” You feel that your governess, Miss Bonner, who tied you to your bed at night as a child, made you more vulnerable to a man like Colin Tennant. Does she still haunt you? No, because I was able to murder her in my novel A Haunting at Holkham [published in 2021]. I got rid of her and there was a wonderful feeling of relief. This is true of a lot of the awful things that have happened to me in my life. Now I’ve written about them, I feel completely different. It’s had a wonderful effect on me. Colin was a Jekyll and Hyde figure, wasn’t he? Great fun at one moment and vicious and violent at the next. Yes. He was wonderful, but he was also dangerous. The whole time you had to be aware of that and anticipate it. It was exhausting. At first, I didn’t know how to cope with him at all. I had my 90th birthday party at Holkham Hall. We ate in the Long Gallery, which is where I had my coming out [as a young woman], watching the Queen Mother whirling to Tommy Kinsman [and his orchestra]. So many memories came flooding back. But I also thought: I’m so glad Colin isn’t here. Why did you never leave him? I wasn’t brought up like that. One tried and tried. After he nearly killed me [Tennant violently beat her on Mustique], our marriage did change. We led more separate lives. He spent a lot more time in the West Indies and I was in England with the children. If we’d had to live cheek by jowl, it would have been much harder, as it is for most people. Are you any closer now to understanding why, when he died in 2010, he left his entire estate to his valet, Kent Adonai? Not really. I just think it was a final cruelty. People do ask if he was gay or bisexual, but I really don’t know. He had a lot of affairs with ladies. He had huge appetites. It was the same with shopping. In India once, he saw these windows on a house. He wanted them, but not a copy. He wanted those very windows. He had a compulsive side. What about Princess Margaret? She’s widely portrayed as having been spoilt and difficult, but you’ve always insisted this is unfair. She was the most wonderful friend to me, because she saw all this [the trouble with Colin] going on. She had some of the same problems herself – I saw how Tony [Lord Snowdon] behaved – and it was worse for her, because she was in the public eye. But she saved my life in a way. She was caring, but she was also practical. She didn’t approve of crying or moaning. You had to pull yourself together. In The Crown, you were played by Nancy Carroll. Did you watch it? Do you still watch it? I did watch it when I was in it. But it’s fantasy. That awful country club swimming pool we sit by! And it’s as if I was pimping for Princess Margaret. All I did was introduce her to someone [Roddy Llewellyn, who became her lover]. What they’ve done is to take a tiny kernel of truth and exaggerate it into something completely false. It makes me so angry. What’s the secret to being so fit and lively at 90? Well, I’ve given up supper. I find that eating late gives me indigestion and I wanted to lose weight around my middle. It’s marvellous. I never feel hungry. I have breakfast and a good lunch and that’s it. I lost a stone without trying. I also walk every day and properly. You’ve got to lift your feet up. What about grief? You’ve suffered terrible losses. I’m lucky that I’ve always had my Christian faith. But you just have to keep going. The pain doesn’t ever go away completely, but it does get better. One thing that did help was to spoil myself by doing something I really loved, like doing my photograph albums or going to a gallery. But I still think about my sons every day. Absolutely I do. What are you going to do next? Who knows? I’m 90 and a half and I do sometimes get exhausted. But I’m having such a wonderful time. Life is so exciting. I’m going on The One Show on Monday. Whatever Next? Lessons from an Unexpected Life by Anne Glenconner is published in hardback by Hodder & Stoughton (£22). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply