Speaking about the hand-me-downs, India said: “It was entirely practical stuff handed from the Queen to my aunt, to my mother.
“I remember my sister and I going through the bags.
“I was the last little recipient of Princess Anne’s chill-proof thermal underwear, thank you very much.
“Actually, I’d like to correct myself. They weren’t even thermal. They were wool, and very scratchy.”
Despite the insight into Princess Anne’s uncomfortable undergarments, the documentary is mainly focused on Lady Pamela and her relationship with the Queen.
Lady Pamela was a bridesmaid at the Queen’s wedding in 1947.
India followed in her mother’s footsteps by also being a bridesmaid at Prince Charles and Princess Diana’s wedding in 1981.
“And then, silence. The Queen’s emotions are all inside, always. She is very strong.”
Speaking about the new ITV documentary, India explained it was “great fun” to film.
She said: “While I knew some of the stories, there were other moments where I was genuinely going ‘really?!’
“It was great fun to do. It always is when I get to do something with my mother.
“She has a real twinkle in her eyes still, and a great spirit.”