Princess Diana’s brother Charles Spencer had mental health treatment after suffering a breakdown while writing his tell-all memoir.

The 9th Earl Spencer, 59, has revealed in his new autobiography ‘A Very Private School’ how he suffered physical and sexual abuse as a child while he was educated during the 1970s at Maidwell Hall boarding school in Northamptonshire.

He has now told BBC One show ‘Sunday with Laura Kuenssberg’ about how he had to seek counselling at a “residential treatment centre” last year due to the “trauma” of reliving the abuse during the writing of the book, which he said sparked a “breakdown”.

Charles added: “Confronting… evil is a very, well, it’s cataclysmic really.

“I’ve always been intrigued by what humans are capable of doing for each other.”

When host Laura, 47, asked how detailing his experiences of abuse in his book had affected him, Charles said he was taken to a “very dark place” – adding:

“I had endless nightmares.”

The uncle of Prince Harry and Prince William also revealed he has not had an alcoholic drink for “many weeks”, and admitted he had undergone EMDR therapy.

It stands for eye movement desensitisation and reprocessing and is a form of therapy designed to reduce the effects of post-traumatic stress disorder.

Charles said on the BBC show he did not feel suicidal after writing the book, but did start to ask “what’s the point” in things as he revisited his childhood trauma.

He revealed in his memoir, published on 14 March, he was molested by a female assistant matron at the age of 11 at the Northamptonshire prep school – describing her as a “voracious paedophile”.