James Middleton has spoken movingly about his battle with depression, calling it a ‘cancer of the mind.’

The Duchess of Cambridge’s younger brother said he hid his problem from his family for many years as he struggled with feelings of failure.

James, 31, said being privileged didn’t ‘make him immune to depression’ and he wanted to speak out to help end the ‘stigma attached to mental illness.’

METRO GRAB VIA INSTAGRAM James Middleton, brother of Catherine, Duchess of Cambridge https://www.instagram.com/p/4l72SIO35-/
James Middleton has spoken movingly about his depression (Picture: Instagram)

He recalled being gripped with a ‘debilitating inertia’ until there came a point when he knew things had to change.

In a candid and moving article for the Daily Mail: ‘I couldn’t communicate, even with those I loved best: my family and close friends.

‘All colour and emotion had leached out of my world and everything was grey and monotone.

‘I know I’m richly blessed and live a privileged life. But it did not make me immune to depression. It’s tricky to describe the condition.

‘It is not merely sadness. It is an illness, a cancer of the mind.

‘I also felt misunderstood; a complete failure. I wouldn’t wish the sense of worthlessness and desperation, the isolation and loneliness on my worst enemy. I felt as if I was going crazy.’

BUCKLEBURY, BERKSHIRE - DECEMBER 25: Prince William, Duke of Cambridge, Catherine, Duchess of Cambridge, Prince George of Cambridge, Princess Charlotte of Cambridge, Pippa Middleton and James Middleton attend Church on Christmas Day on December 25, 2016 in Bucklebury, Berkshire. (Photo by Samir Hussein/Samir Hussein/WireImage)
James said for a time he found it hard to speak to his family, including sister Kate and brother-in-law William (Picture: WireImage)
METRO GRAB VIA INSTAGRAM James Middleton, brother of Catherine, Duchess of Cambridge https://www.instagram.com/p/4l72SIO35-/
James and his dog Ella, who is now a Pets As Therapy dog (Picture: Instagram)

James said he struggled throughout school with dyslexia, which meant he ‘permanently lagged behind.’

Last year, he was also diagnosed with Attention Deficit Disorder (ADD) and his mind often ‘wanders off.’

He said the two combined meant he had wonderful creative ideas and intense emotions, but would find it hard to follow through with the minutiae of running a business or mundane tasks.

James said the clinical depression first hit at the end of 2016 and his mental health deteriorated for a year before he sought help.

He said much of 2017 was spent ‘in a fog’ in which he ‘barely functioned, stopped talking to friends and went through the motions of living but achieved nothing at all.’

The businessman then acknowledged he needed help and contacted his GP.

He then packed his four dogs into the car and drove to the Lake District where he took long solitary walks and swam in the icy waters of Coniston Water.

WINDSOR, UNITED KINGDOM - MAY 19: (EMBARGOED FOR PUBLICATION IN UK NEWSPAPERS UNTIL 24 HOURS AFTER CREATE DATE AND TIME) Michael Middleton, Carole Middleton, James Middleton, Pippa Middleton and James Matthews attend the wedding of Prince Harry to Ms Meghan Markle at St George's Chapel, Windsor Castle on May 19, 2018 in Windsor, England. Prince Henry Charles Albert David of Wales marries Ms. Meghan Markle in a service at St George's Chapel inside the grounds of Windsor Castle. Among the guests were 2200 members of the public, the royal family and Ms. Markle's Mother Doria Ragland. (Photo by Max Mumby/Indigo/Getty Images)
Michael Middleton, Carole Middleton, James Middleton, Pippa Middleton and her husband James Matthews attend the wedding of Prince Harry to Meghan Markle (Picture: Getty)
Mandatory Credit: Photo by People Picture/Foudre/REX/Shutterstock (9971220bn) James Middleton GQ Men of the Year Awards, Berlin, Germany - 08 Nov 2018
James said his privileged background did not make him immune to depression (Picture: Getty)

Upon his return, he gave his GP permission to speak to his family, now sees a psychiatrist and has had sessions of cognitive behavioural therapy (CBT) to change the patterns of his thought process.

James said he struggled to speak to his family, including sisters Kate and Pippa and brother-in-law Prince William, about how he felt.

He added: ‘You may wonder why I didn’t confide in them, but those who are closest to you are the hardest to speak to. It was impossible to let my loved ones know about the torture in my mind.

‘Equally anything they’d have said would have been rebuffed.

‘That’s why I withdrew from them, repelled their well-intentioned advice and finally stopped answering their calls and texts.’

Since his battle with depression, James says his new mantra is ‘It’s OK not to be OK’ and he and his dog Ella now volunteer with the Pets As Therapy charity.

He is also backing Kate, William and Harry’s movement Heads Together, which works to ensure people feel comfortable talking about everyday mental health and well-being.