Louis has been to San Francisco, a city that was once the centre of the gay-rights movement and is now blazing a different trail. For Louis Theroux: Transgender Kids, the last in his current run of BBC2 documentaries, he met Camille, a charming, articulate five-year-old who until a month ago was known as Sebastian. When asked about her gender identity now, Camille is firm and clear “not a boy and a girl anymore, not transgender… a girl”.

Interviewing children and teenagers about such a sensitive and controversial subject must be the ultimate test of the new tactful Louis, and he passed, playing “battle dance” with Camille (her Lady Gaga impression was spot on) and sharing personal stories with his older interviewees. “When I was 14 and turning 15, that was probably the hardest year of my life, it really was…” he told 14-year-old Nicki and she seemed genuinely comforted by this admission.

For the moment, though, it is the parents, not the kids, who face the most difficult dilemma: do they begin the process of medical intervention at a stage when their child may be still experimenting with their identity? Or do they hold off until later and allow their child to go through the trauma of puberty in the “wrong” body? It’s an either/or decision that doesn’t seem to allow for a gender spectrum, along which children like Crystal/Cole may move over the course of their lifetime.