Prince and her have forged a remarkable friendship in the past few weeks

When, later on Sunday, Prince Harry strides across the forecourt of Buckingham Palace to welcome an exhausted team of injured former soldiers, it will be a moment of quiet triumph for all concerned.

Despite terrible disabilities, the brave half-dozen will have completed a shattering 1,000-mile journey from the north of Scotland to London to raise money for his charity, Walking with the Wounded.

It will be a cheering moment of satisfaction for Harry, too. Whatever the criticism wilder antics draw, no one can doubt his commitment to the cause of injured veterans.

Scroll down for video

Kirstie Ennis, a 23 year old Helicopter door gunner, pictured with Prince Harry is the only woman on the Walk Of Britain

But among the small group of warriors drawing breath at the special reception laid on for them, none should feel more proud than Kirstie Ennis, an Afghan veteran like Harry, and the sole woman to take part in the 72-day expedition.

She is lucky to be alive. Surgeons have practically rebuilt her in the course of 38 separate operations. She has somehow covered the extraordinary distance on a leg so damaged and painful that her medical team insists it should be amputated – and it will be removed once today’s final agonising mission is complete.

It is just three years since the slender blonde was told she would never walk again. In fact, so exemplary is Kirstie’s determination that she and the Prince have forged a remarkable bond in the past few weeks, when Harry joined 24-year-old Kirstie and the other walkers on their journey.

Today, speaking for the first time about their friendship and what it means to her, she offers a rare insight into the way the 31-year-old Prince goes about his job.

There was one moment, she says, when he dared to complain about his painful knees and got a fierce ribbing in response.

It is, though, her own story which is truly compelling.

Kirstie’s life changed for ever on June 23, 2012, the day when her massive Sikorsky CH-53E Super Stallion helicopter crash-landed in Afghanistan. Miraculously, she survived, but without a jaw and missing half her face, destroyed when her 50-calibre machine gun smashed through the left side on impact. Then there were the smashed legs and arms, the brain and spinal damage.

Her career with the United States Marine Corps was over.

‘We still don’t know what happened,’ she explains quietly, ‘but we lost control and were free falling at 150ft per second.’ Kirstie had been posted as the door gunner.

‘We crashed to the ground and all I remember thinking is “I’m gonna die”. Then I was out cold.

‘The backside of my rifle went through my jaw.

‘I remember opening my eyes and all I could hear was screaming. I couldn’t breathe because of the blood in my throat and nose. I could feel my teeth crumbling in my mouth. We’d picked up a medic during the mission and he stayed with me and told me not to close my eyes, or I’d be gone. I owe him a lot and I didn’t blink until we got back to Camp Bastion.

‘I think everyone thought it was game over. I was so scared I was vomiting on myself out of pure fear. That was the day I knew I would be different for ever.’

Kirstie was due to have an amputation below her left knee this summer so that surgeons can fit a more comfortable prosthetic.

But she bravely postponed the operation especially to take part in this expedition, opting instead to wear a carbon-fibre leg brace. At £10,000 it is an expensive piece of kit. Yet she is in constant pain. ‘I’ve been in this leg brace since April,’ she explains.

Kirstie is lucky to be alive and surgeons have practically rebuilt her in the course of 38 separate operations. She joined Prince Harry for a walk in Shropshire

‘I can’t walk more than a quarter of a mile without it and I can’t run. My feeling is if this leg’s going to impede me then let’s get rid of it.

‘For me it’s about quality of life. I want to have kids one day and be able to run around the yard with them. Having this brace is a constant reminder of what I can’t do.

‘When I told my doctors I was not going to have the operation until later in the year they were pretty stunned, especially when I told them I was planning to walk 1,000 miles across Britain. It is the hardest thing I’ve done apart from my rehabilitation.’

She completed the shattering 1,000-mile trek on a leg so damaged and painful that her medical team insists it should be amputated – and it will be removed once today’s final agonising mission is complete

This is the fourth expedition for Walking with the Wounded, and Prince Harry has been on all of them, visiting North and South Poles and Everest. The Walk of Britain has so far raised nearly £40,000 from public donations.

Aside from Kirstie, the team comprised British soldiers Stewart Hill, Matt Fisher, Alec Robotham and Scott Ransley and American former serviceman Andrew Bement. All have physical or cognitive injuries sustained in the line of duty.

Today, Kirstie is the picture of health. Tanned, and with her blonde hair swept up in a ponytail the only evidence of the trauma is a scar on the left side of her face and of course her leg brace. She has refused to let her injuries destroy her life.

After three years of rehabilitation including speech therapy, she has an MA in business studies and psychology and is a qualified stockbroker. She has been with her boyfriend Brian, a fellow former Marine who was terribly injured in a bomb blast, for a year.

Despite the damage to her legs, she is an expert snowboarder and has just been named in the national team for paralympic swimming.

She plans to compete in the pool in Prince Harry’s Invictus Games for wounded servicemen and women in Orlando next spring.

‘Confirmation about the national team came through while I was walking with Prince Harry in Norfolk. Harry was really proud and very excited for me. He loves to see veterans excel and overcome their disabilities, that’s what drives him and you can really see that.’

Kirstie had first met met Harry at the Warrior Games in Colorado in 2013, the inspiration for his Invictus Games. But it is only in the past few weeks that they have come to know each other.

‘He seems so engaged and committed. He wanted to know my story and I felt I could open up to him and that he really listened. It was just like walking with a friend, or a brother.

‘The military is a family in that respect. It’s a brotherhood. It really meant something to have Harry walk with us. There were no feelings of superiority. We spent two days together, one walking in Shropshire where we kicked a ball around with [former American football star] Dan Marino which was pretty surreal and another day walking in Norfolk which was so beautiful and very special. There were no cameras that day and I told Harry about my time at Camp Bastion because we were serving in the same place at the same time.

‘We talked about our shared love of aviation and I asked him when he knew he wanted to be a soldier.

‘He said from when he was a little boy and that it had always been his dream and that the military has been the greatest thing for him. I was the same when I was a kid. All my dolls were dressed in Marine Corps clothes.

‘He’s so down to earth and very easy to get along with and he fitted right in with the group, especially with Scott (Ransley) who is blind in his right eye. He’s also very kind and when people came up to say “hi” he made the time for them, especially the kids and you could see it really made their day.

‘He wanted to know about my family. My mum and dad are both former Marines and I told him my mum is a big fan of the Royals and that she loved his mother Princess Diana. I also teased him that I’ve probably seen more baby photos of him than he has and he laughed about that. Everyone at home is tickled that I got to meet Harry and walk with him.

She recalls how the group teased him when he dared to complain that his knees were aching at the end of one 15-mile walk. ‘He was limping at the end and complaining a bit, but quietly as he knew we would have given him grief,’ she laughs.

Walking up to 18 miles a day has been a challenge for the whole group, but having him alongside them lifted their morale, she says.

‘It’s not been easy. With my injuries I deal with pain constantly and it affects me physically and emotionally. I’ve never felt as disabled as I have done on this walk. It has been so hard. It was great when Prince Harry joined us.

‘It’s been a long trying road. The crash left me with so many injuries, mental and physical. I’ve basically had my face rebuilt. As a young woman I was dealing with a disfigured face, my neck, back and legs were in braces and I thought “I will never be the same girl again’’.

‘I’ve not got the same body I was born with, but they’ve done a great job. I used to be embarrassed by the scars on my face.

Kirstie’s life changed for ever on June 23, 2012, the day when her massive Sikorsky CH-53E Super Stallion helicopter crash-landed in Afghanistan

‘I used to not like smiling because I didn’t have a jaw or my teeth. It was so hard, a constant reminder of the things that happened. Now it’s a reminder of what I’ve overcome. I wouldn’t change anything. I’ve been given two shots at life and actually in some ways I’m thankful that this happened to me because it has made me a stronger person without a doubt.

During the walk, which has toured through much of Britain, Kirstie has been placing ‘dog tags’ – replicas of military identification tags – in memory of the colleagues she has lost, along the route.

‘Harry and I spoke about this and he’s determined to do what he can to help those who come home from war and are suffering post-traumatic stress. It’s a real issue at home.

‘Harry asked if he could lay one with me in Shropshire. We stopped at a castle for lunch and left one of the tags at a war memorial we found in the grounds along with a poem, which Harry read.

‘The idea is that they laid their lives down for strangers, now strangers will come across these tags and honour their memories and legacies. Harry really got it and he really understood me.

‘It’s surreal. I’ve visited the Palace as a tourist and had my picture taken there.