The Duke of Sussex has described his emotional “unravelling” after he returned from military service in Afghanistan in 2013.

In a Netflix documentary series about the Invictus Games, Prince Harry said the “biggest struggle for me was that no one around me could really help”.

The “trigger” for the duke’s trauma had been serving in Afghanistan.

But he linked it to the loss of his mother Princess Diana, who had died in 1997 when he was 12 years old.

“Losing my mum at such a young age was trauma that I had that I was never really aware of. It was never discussed, I didn’t talk about it and I’ve suppressed it like most youngsters would have done,” said the duke, 38.

“Unfortunately like most of us, the first time you really consider therapy is when you’re lying on the floor in the foetal position, probably wishing that you dealt with some of this stuff previously.”

The five-part documentary series, Heart of Invictus, tells the story of the duke’s sports competition for servicemen and women who have been injured and disabled.

Prince Harry said he wanted Invictus to be like a safety net to catch people, because he lacked the support or understanding of his own “invisible injuries”.

“I didn’t have that support structure, that network or that expert advice to identify what was actually going on with me,” he said.

An injured veteran tells the duke about the “demons” that have haunted him and held him back.

And in response Prince Harry explained that in his own experience the loss of his mother had left him with “no emotion. I was unable to cry, I was unable to feel, I didn’t know it at the time”.

But he described the “chaos” when those suppressed feelings were released in later life.

“My emotions were sprayed all over the wall, everywhere I went. I was like: ‘How the hell do I contain this? I’ve gone from nothing to everything,’” he said.

The prince emphasised to contestants the importance of removing stigma around discussing mental health – or what he called “mental fitness”.

“The more it makes people feel uncomfortable, the more we need to talk about it,” he said.

The documentary series shows the physical and psychological challenges facing injured military veterans, as they prepared to take part in the Invictus Games, first launched by Prince Harry in 2014.

He speaks of the games as being his response to the shock of seeing casualties in the war in Afghanistan and his feeling that the public were not fully aware of the reality of the conflict.

He toured Afghanistan twice. His first tour in 2008 ended abruptly when a media embargo was broken, while his second tour of four months ended in January 2013.

There are now contestants from 23 countries and a number of injured veterans talk about the importance of the games as an uplifting force in their recovery, in a documentary that follows their often emotional journeys.

The next games will be held in Dusseldorf in Germany next month and the series focuses on the rising numbers of Ukrainian service men and women with injuries following the Russian invasion.

Prince Harry will be at the games in Germany, where it is expected he will be joined by his wife Meghan, who appears briefly in the documentary.