Let’s move on to your first choice, which is Andrew Morton’s famous biography Diana: The True Story.

This is a book that was familiar to me from the start because it was so famously serialised. I read it during a holiday to the South of France the summer before I started writing my book because I knew that it was going to be an invaluable way in to understanding the Princess of Wales. I think you cannot begin to write a book about William and Harry without understanding their mother because there is so much of their mother in them. And I surprised myself by how much I actually enjoyed reading it. It felt a little bit like a guilty pleasure.

It is not necessarily the most beautifully written book but it is packed with so much colour and information which enabled me to understand Diana at probably the most difficult time of her life. This was during the lead up to her separation and she was a woman who was so desperate to make her marriage work. But, of course, she didn’t stand a chance because Camilla had always been on the scene.

There are those immortal words – in her Panorama interview with Martin Bashir: ‘Well, there were three of us in this marriage, so it was a bit crowded.’

Yes, exactly. And I think this book really provides a valuable insight into Diana and what was going on and the impossible task she faced of being married to a future king who had a mistress who was the one he really loved. Morton also has some fascinating snippets in the book about William and Harry and he also talks about the boys.

What kind of impact do you think the split had on the boys?

I think Harry was largely protected because he was the youngest and he was still at Ludgrove. But I think it had more of an impact on William because he was aware of what was going on and that is something that Morton looks at. Diana really used William as a confidante and invested a lot of her emotions in him and I think that must have weighed very heavily on William. He took on a lot for such a young boy who had always been so carefree and happy. I think that changed his character. And, of course, you have to remember that, even though lots of children have parents who get divorced, this was being played out so publicly. When his mother gave that famous Panorama interview on the BBC he was teased and it was a humiliating experience for him. I talk in my book about the fact that he really never actually forgave his mother for it. She had embarrassed the whole family and it had made life very difficult for him. Simone Simmons, a complementary therapist and confidante of Diana, who I interviewed for my book, said it was the one time they really fell out. It took a while for William to really get over that.

I am not surprised. Well, next up isThe Housekeeper’s Diaryby Wendy Berry, a book that was banned in Britain.

When it said banned in Britain on the cover I knew it was a book that I had to read. It wasn’t easy to get a copy. I think it may be out of print but eventually I managed to track one down. Wendy Berry was the housekeeper at Highgrove and Kensington Palace for many years and most importantly during the break-up of Charles and Diana’s marriage.

I found the book to be really compelling reading. I devoured it within a day. It was full of fascinating colour and really great anecdotes. I particularly like the story about how Diana and Charles tried to keep the pretence of the marriage going as much as they could by pretending they were sharing a marital bed.