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 spa…