Viewers will see Harry Potter author JK Rowling break down in tears as a cherished family story is punctured in the new series of Who Do You Think You Are?
The famously private writer said the early death of her mother was one of the reasons she agreed to go through the "very emotional experience" of researching her family tree for the BBC1 show.
She told the Radio Times her mother Anne, who died aged 45 in 1990, was "very interested" in her French roots but never got the chance to explore them.
Rowling (46) said: "So a huge motivation in looking into my family history is my mother. It's very much bound up in that loss."
The writer said she was "braced" for surprises in the show which follows celebrities tracing their family trees.
She said: "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."
One of the most emotional moments came when Rowling discovered the family story about her great-grandfather winning the Legion d'honneur for his bravery in the French army was not true.
The writer, who herself was awarded the medal in 2009 for services to literature, even mentioned her relative, Louis Volant, in her acceptance speech.
The show uncovers that the Louis Volant who won the medal for an act of wartime bravery is not related to her and the keepsake treasured by her aunt is not an award for bravery but probably a badge from the former wine waiter's trade union.
She said: "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."