He swam in Coniston Water, took lonesome walks and stayed in a remote cottage with his dogs.
He acknowledged that although he was “richly blessed” and privileged, he was still not immune to depression which had made him feel “like a complete failure”.
Although he did not contemplate suicide, he revealed he “didn’t want to live in the state of mind I was in either’”
As a young man, he constantly had difficulties with his studies and when he moved to board at Marlborough College, where both his sisters attended, he became “horribly homesick”.
“Catherine (Kate) had already left for university by the time I got there, but having Pippa around was a comfort.
“Even so, I didn’t fit in… I was given longer to finish my exams [due to dyslexia], which was a waste of time. It just meant I had more time to realise I couldn’t answer the questions.”
Mr Middleton, who now owns his own personalised greeting card company Boomf, said confronting the fact that he needed help had given him hope, and he had wanted to speak out about his plight after feeling compelled to do so by the inspiring work of the Duchess, Prince William and Prince Harry with their mental health charity, Heads Together.