Beverley Turner with two of the former couple's children Croyde and Kiki

Fifteen years ago, Beverley Turner looked on with pride as her husband stepped on to the podium in Athens to accept his second Olympic gold medal.

In a moment of fatherly exuberance, a jubilant James Cracknell swept his baby son Croyde into his arms as he celebrated his win in the coxless fours (he'd won his first four years previously in Sydney).

'As long as I wake up beside him tomorrow morning, I'll be happy,' said Beverley, in the post-win, celebratory glow.

Contrast that with this weekend, when 46-year-old Cracknell became the oldest winner in the Boat Race's 190-year history, rowing for Cambridge University, where he is studying for an MPhil in human evolution.

It should have been a moment of triumph: but this time, on Sunday, the Cracknell children, Croyde, now 15, and daughters Kiki, ten, and Trixie, eight, watched the race with their mother at a friend's home.

'The kids needed to see that this enormous family sacrifice wasn't entirely in vain', Beverley, 45, wrote yesterday in an extraordinarily honest, unvarnished account of the breakdown of the couple's 17-year marriage — which has rather taken the lustre off his win.

'James has spoken publicly about this latest feat, demonstrating to his children that you can do anything you set your mind to.

'He won't mind me admitting I consider that b******s. I wouldn't want my children to view such an exit from familial responsibilities as something to aspire to.'

James Cracknell grins with delight after finishing the Boat Race on Sunday. He was part of the Cambridge University Boat Club Crew, which one the annual event

In the piece, published in The Times, she details not just the impact of life after a brain injury (James was put into an induced coma after being hit by a truck in July 2010), but also how the strain of being an Olympic calibre sportsman — and of being married to one — took its toll. It all must make deeply uncomfortable reading for Cracknell.

In the article, Beverley wrote of fearing the 'dreadful example' they were setting their children of married life, of her deep-rooted fear of being 'ground down', and of the 'absolute dereliction of parenting and marital duty' that training for the Boat Race had entailed — along with details of 'snapping, sighing, arguing and slamming doors'.

While she said their relationship was — and still is — one built on 'mutual respect and admiration', she also chronicled behaviour that anyone can see would put strain on a marriage.

'When James spent 50 days rowing across the Atlantic with Ben Fogle in 2005, he failed to discuss his plans with me in any detail despite us having a two-year-old son,' wrote Beverley. 'The difference in 2018 was whether I could reasonably live with these exhausting, self-centred pursuits for the rest of my life. I prefer the journey to the destination . . . James is all about the target.'

She insisted she does not put the end of their marriage solely down to his personality changes. She admitted that it had not been perfect before his brain injury because of the frustrations which can arise from being married to an 'extremely driven man'.

'As any woman will admit, there comes a time when you are sick of waking up alone on holiday because these alpha males are already at the laptop or on the rowing machine,' she said.

'Twice we went to Barbados and James spent three hours a day on the running machine inside the hotel. Most women want a partner to drink Buck's Fizz with on the beach. We don't want a man who's fitting in gym sessions around kids' club hours.'

James Cracknell was seen heading to a gym in London on Monday, a day after his Boat Race triumph. His estranged wife Beverley Turner was also in the mood for keeping fit - she headed out for a jog

The broadcaster, herself once a competitive swimmer, also revealed that she had been 'sure he would fail' to compete in the Boat Race, as it was 'ludicrous to think he could regain the strength and stamina required to sit alongside 20-year-old rowers'.

In the piece, Beverley also wrote candidly about the impact of her husband's accident.

In 2010, just after becoming the highest placed Briton ever in the gruelling Marathon des Sables, Cracknell nearly died. He was cycling across America, on another endurance challenge, when he was hit by the wing mirror of a petrol tanker travelling at speed.

It caused his brain to slam forward, crushing the frontal lobes — the part of the brain that controls personality. He was put into an induced coma, regaining consciousness in a hospital in Phoenix, Arizona, a few days later.

Beverley, who has her own antenatal class business, has spoken openly about the accident, of being in a Las Vegas hotel when she received the phone call that turned life upside down.

Doctors warned her that she might see changes in her husband, including an inability to read emotions, irascibility, laughing or crying out of context, and arguing.

Those warnings, it turned out, were frighteningly accurate. (She explained: 'The aftercare the NHS provides for the brain injured is hopeless.')

Yesterday she wrote: 'After a brain injury, a couple's dynamic typically becomes one of parent and child: complete with nagging, resentment and sulking.'

She added: 'When I told a friend that James was off to Cambridge, he said: 'You never know, you might miss him.' I replied: 'But I've missed him for eight years.'

She continued: 'The problem with a brain injury is that the supporting partner is never entirely sure what can be attributed to the condition and what is just your partner being a d***.'

Happier times: James and Beverley married in 2002 but his ceaseless desire for success eventually drove a wedge through their relationship

She also revealed that James's appearance last year on reality TV show Celebrity Island had been a welcome break, and that 'the calmness that descended on the house during those six weeks was illuminating for me. Yes, single parenting is incredibly hard, but the house was oddly more oxygenated for all of us.'

This latest piece is not the first time Beverley has detailed the problems in their marriage. The couple also wrote a book about their experience called Touching Distance, in which they discussed the impact of the accident on their marriage.

In interviews they have referred to a statistic: 75 per cent — the percentage of marriages in which a person sustains a brain injury that end within three years.

'Look, we're lucky,' she told The Sunday Times. 'He should have been dead. Yes, there are days when I think, 'How can I live with this for ever?' But I probably will. That's probably good enough.'

The inclusion of the word 'probably' was, in the end, an echo of what was to come. Beverley, a high-achiever who put her own career on hold at the beginning of her marriage to support her husband's sporting endeavours, heralded her account of the disintegration of her marriage on Twitter. 'Behind every great man an' all that...' she tweeted on Sunday.

Anyone who has read of the couple's journey since that fateful day in July 2010 will know that Beverley has been crucial in her husband's recovery.

The couple first met in the Jordanian desert, where they were chained together for two hours in a Bedouin tent for a television programme. Cracknell was riding high after his first Olympic gold in 2000 and Beverley was an up-and-coming sports television presenter. They got engaged soon after. He proposed in Croyde Bay in Devon — hence their son's unusual name — and married in 2002 at Clearwell Castle in the Forest of Dean in Gloucestershire.

She once laughed about how he would select a target on a map and put his foot down until they arrived. 'James needs a goal, and pity the person who stands in his way,' she said, in 2009, less than a year before his accident.

She does not blame her husband's brain injury for the end of her marriage: 'That's too simplistic — it wasn't perfect before.

'I have spent many evenings in the company of Olympic medallists and it's obvious to me that such ambitions rarely arise from a healthy psychological place.

'Having to endure physical and emotional torture to prove oneself on a global stage starts as a blessing, but its inescapability is often a curse. How can these characters ever truly be happy when nothing but external validation drives them on?'

Long accustomed to the strains of being married to an elite athlete and perpetual adventurer, the pressures that have long over-shadowed the Cracknell marriage must have become unbearable for them to have parted.

As Beverley wrote yesterday: 'My father talked to me recently about 'pebbles on the beach that rub together over the years until the corners are knocked off and they sit smoothly together'.

'But Dad,' I said, 'that literally means being ground down. And I can't do that.'

As far back as 2005, a year after that jubilant moment of familial pride in Athens, Beverley was openly speaking of the 'massive rows' that preceded the first of her husband's post-Olympics challenges — his Atlantic rowing expedition.

'Look, I married a rower, but I didn't marry Sir Ranulph Fiennes,' she said in an interview with the Mail. 'It is only in the last couple of weeks that I have reconciled myself to the fact that he is going — and that he has his reason for doing it.

'It is the right thing for him to do at this stage in his life; but it is hard, especially after I've been so good about his career. We've made endless sacrifices, never having a weekend in five years, never having a holiday, having so little time together. And now this.'

They weathered that storm (Cracknell and Fogle took 49 days, 19 hours and 8 minutes to complete the challenge), and Beverley was a tower of support as her husband went on to complete the London Marathon, a race to the South Pole (with Fogle again), the Marathon des Sables, and more. And then came the accident.

James and Beverley attended the annual Pride of Britain Awards together last month

Beverley was warned her husband might not recognise her (he did), but when they flew home four weeks later, it didn't feel like a celebration.

While Cracknell's physical recovery went well, the mental challenges, including bouts of epilepsy and behavioural changes, were harder to overcome. He became irrationally strict with his children, there was a terrible outburst when Beverley was five months pregnant and he had his hands around her neck.

'Even as I looked into his eyes, I felt sorry for him — he was the one in the grip of a dreadful condition,' she said in 2014.

But instead of taking it easy, Cracknell was spurred into yet more feats of endurance. Within six months of the accident, the couple were discussing his next challenge: another bicycle race. If anything, it would seem, the athlete's determination post-brain injury has become steelier.

He started to apply for university courses after appearing on Celebrity Island with Bear Grylls last year, but at the same time his wife noticed his 'behaviour had deteriorated'.

She took him to a neuropsychologist, who told them Cracknell had 'tunnel vision' and that 'frontal-lobe injury makes you more of yourself'.

Having won a place at Cambridge (a year after attempting to become an MEP candidate), the strains on the couple became too great.

And what of the rower in all of this? Before the split was announced, Cracknell spoke of his determination not to be seen through the prism of the accident.

'I had some bad characteristics before the accident as well, so it's not fair to label being stubborn and selfish on the truck driver.'

Last week he told BBC Radio 5 Live they had tried everything to hold it together. 'We're also, as any couple is, different people from who we were 17 years ago and we can look back and saw we did everything.'

As for his brain injury, he said: 'It's not like the accident was last year, it was nine years ago, but I guess there's an element of if you're the partner you always judge your other half through the prism of what has happened.

'As a sportsman, you are slightly single-minded and stubborn, which is great if you're the sportsman but not great to live with. So if you become more of that, that's an issue.'

His wife, meanwhile , insists there is 'no animosity'. Even though they were separated, the family spent Christmas together.

One suspects the rower will now be looking for his next challenge, but he is clear on one thing: 'But for Bev, I wouldn't be here now and able to be who I am now.'

Had he only realised that earlier in the couple's troubled union, the marriage might still be afloat.