James Middleton has credited the mental health work of his sister the Princess of Wales and her husband the Prince of Wales for helping him “move forward”.

The entrepreneur and mental health advocate has previously spoken about his “rebirth” from depression after undergoing therapy.

He has recently written the book Meet Ella: The Dog Who Saved My Life, about his pet being his “reason for being” as well as helping to change his mindset and provide him with moments of reprieve.

Middleton told ITV’s Lorraine that “my family were the hardest people to speak to” about the crisis he was going through, as they know him in “many ways better than I knew myself”.

He added: “I initially went into therapy and, at the right time, my family got involved. I was very fortunate they did because they did have to be patient, they had to sit on the sidelines and really watch and see me suffer.

“It was very challenging for them too because all they wanted to do was help, of course, and then when the timing was right, and I think timing was so important, they came in, and they understood, and they were able to understand a lot more than I actually thought.

“I recognised that the work that both Catherine and William have done in mental health and that helped me move forward.”

Kate’s work has focused on mental health and the early years of childhood in recent years, and both she and William regularly raise awareness of mental health projects.

James Middleton said his dog Ella ‘introduced me’ to his wife Alizee Thevenet (Mike Egerton/PA)

Middleton said at first he did not speak about his struggles as he saw it as a “stigma”, and also thought “I had a very privileged upbringing, (I’ve) been very fortunate about my schooling, and had huge support and love (from) my family”.

But he added: “Depression is significantly more than just a feeling. It is an absence of feelings. It is class-less, it’s race-less, it’s gender-less.

“Depression… (is) still the largest killer of men under the age of 50. I wanted to share my story in the hope that it might resonate with them.”

After his dog died, Middleton says he was concerned that she would become a “memory”, but he now sees the animal through his one-year-old son Inigo’s eyes as Ella “introduced me to my wife”, Alizee Thevenet.

Recalling introducing his partner to his family, Middleton added: “We are a relaxed family and I think I threw Alizee a little bit in the deep-end in that scenario, but I think (we’re) fortunate in the way that we’re such a close-knit family, and it was a moment that I think for her was more challenging or embarrassing than it was for me.”