To say that Runcie was given unusual access to a process that usually takes place well out of the public eye is to put it mildly. He's there as Rowling completes a 17-year process and types the final words of "Deathly Hallows."
Or so, at least, he seems to be.
I'm a documentary purist, yet part of me hopes that this one bit might have been at least partly staged, writing not being a process that usually benefits from having a camera trained on it.
Not that Rowling - known in her off-the-page life as Joanne - doesn't sound like a writer.
"It might be rubbish," she says when Runcie congratulates her.
And already she's steeling herself for criticism.
"For some people to love it, others must loathe it. That's just in the nature of the plot," she says. "There's so much expectation from the hard-core fans that I'm not sure I could ever match up to it."
Runcie's no Ted Koppel - the film begins and ends with his administering a version of the Proust questionnaire to Rowling, whose idea of perfect happiness turns out to be "happy family."
And he may stretch the boundaries of even pop psychology at times in trying to link the circumstances of Rowling's early life to Harry's.
Because while there may have been a cupboard under the stairs of the house in Bristol where she spent her early childhood, it's not as if she were required to sleep there.
Still, Rowling, who's been generous with her time with her young fans and more sparing with reporters, comes across as an intriguing figure, if only because, after many trials of her own, she seems like Harry, to be finally happy.
Remarried and the mother of three, she's seen enjoying a life without deadlines for the first time in a decade.
