The Harry Potter author is among the famous faces taking part in the new series of the popular BBC genealogy programme. As part of her quest for information, Rowling sets out to discover more about the prestigious Légion d'honneur, an honour awarded for bravery to her great-grandfather Louis Volant.
Speaking to the Radio Times, Rowling admitted that she had been "braced" for some surprising discoveries after agreeing to take part in the show; a decision she made due to her mother's death at 45.
"Mum died when I had just started writing Harry Potter. It's a real regret that I never even mentioned it to her, that she died without knowing anything about something so huge," she explained, adding that Anne, who suffered from multiple sclerosis, "was very interested in her French roots but never had a chance to explore them. So a huge motivation in looking into my family history is my mother. It's very much bound up in that loss".
The 46-year-old continued: "I probably felt as everyone does when they agree to be the subject of this programme: excited, apprehensive, very curious, definitely nervous... I think I cried on three separate occasions - I don't know whether I've set a record."
In 2009, Rowling collected her own Légion d'honneur award from French president Nicolas Sarkozy. While accepting the honour, she spoke of her happiness at bringing a second into the family.
However, after admitting her own doubts about the authenticity of the badge her great-grandfather won - now kept by an aunt - Rowling was soon to discover that her suspicions were correct. The award Volant had secured was believed to be a common one, awarded from his trade union.
"She became very concerned," director Leo Burley recalled. "This was a family story that had been told not just by her mother, but by everyone. She found it embarrassing and was worried about how things were going to turn out."
However, Rowling remained positive about her experience on the show: "There were a lot of big surprises, some wonderful, and one rather upsetting. However, I went into the programme wanting the truth, no matter what it was, because I knew so little about my French ancestry, and I don't regret a moment of it. I loved the whole experience.
"The story both was, and wasn't, what I expected. It is inevitably a very emotional experience. I can't really explain why what happened to our ancestors means so much to us but I found myself so caught up in their stories, and so worried about them, even though they are beyond my help now.
She added: "It is humbling to see yourself as a tiny part of a huge family tree - but it's also strangely reassuring."
Who Do You Think You Are? returns to BBC One on Wednesday, August 10 at 9pm.
> Ten Things About... JK Rowling
> JK Rowling's childhood home up for sale