• She left behind husband St John and two young sons, Reef and Finn
• Her checklist for them included having boys roller skate in a museum
• Her story, based on St John's book, is now a new movie, Mum's List
It could be any family's happy home video: a couple and their two young sons chase across an English beach in the summer sunshine before scooping up their laughing, shrieking children in a family embrace.
Too perfect, perhaps - because as he watches the scene unfold through the gloom of a cinema screening room, St John Greene's eyes fill with tears.
There, in the opening sequence of a major new film, is his late wife Kate, played with unbearable realism by actress Emilia Fox.
"I bawled my eyes out when I saw the film for the first time," he admits today.
"She really did Kate proud. She captured her exactly. That smile. Her exuberance. The passionate, all-consuming love for our kids. It was like watching Kate return to life."
It is a matter of huge emotion, naturally, yet also a source of pride, not least because the new film, Mum's List, is based on St John's own best-selling book of the same name.
The story of Kate Greene's courageous battle with cancer and the moving 100-strong list of hopes, ambitions and instructions that she wrote for her husband and sons days before she died has captured the public imagination, selling more than 100,000 copies in two just two months.
Four years on, and the story has grown into the new film starring Emilia Fox, and Rafe Spall as St John battles to build a new life without her.
St John, or Singe as he is known, has more than fulfilled his promise to his dying wife, bringing up his sons Reef, now 12, and Finn, now 11, with the same spirit of joy and adventure.
Thanks to Kate's list, family life means proper meal times and scuba diving, hunts for four-leaved clovers and roller skating through the halls of the Natural History Museum, a glorious mix of domesticity and ambition.
There was a time when the Greenes had led a charmed, outdoorsy existence in Somerset. Kate, who had worked in insurance, and Singe, a paramedic, loved to explore the countryside and travelled extensively.
But early one August morning in 2008, Kate hesitantly told St John she had found a lump in her breast. And from that moment, things changed for ever. Her husband was optimistic at first, telling her it was probably a cyst. After all, the lump didn't feel much bigger than the tip of a pencil.
But a scan led to an immediate biopsy and then the terrible news Kate needed a full mastectomy - immediately. Though initially she was told she had a high chance of survival, by the end of 2009 it was clear Kate was deteriorating daily. She lost her blonde hair and was in constant pain.
By early January 2010, the cancer had spread to her lungs and bones, and palliative care, the Greenes were told, was all that remained.
Barely eating, her speech badly affected, Kate was admitted to Weston General Hospital. Not that Kate had ever forgotten her sons, then six and five, or the future they still had, and one night she told St John she wanted to leave a list of hopes and wishes for the days and years to come.
It ranged from the eminently sensible to the thrilling: "Try not to let them go into the Forces; always kiss the boys goodbye and good night; buy a family dining table so you can have meals together."
Item by item, she set down her hopes for her children's future.There were requests for skiing and boating; trips to see the Northern Lights and international sports fixtures; camping, caravanning and picnics in favourite places. And, poignantly, a request her husband find a new wife to help bring up her boys.
On the morning of January 20, 2010 a nurse phoned Singe with the words he had been dreading.
"Kate's taken a very bad turn for the worse," she told him.
"I drove like a maniac," he recalls.
"Kate was in a private room surrounded by five nurses. All I could think was, 'Thank God I wasn't too late'."
He held her hand and kept talking to her even when her breathing stopped. She was just 38.
That, however, was not the end of her story. When the news of Kate's list emerged, it provoked huge interest around the country - and when a ghost writer then suggested she help Singe write a book, he agreed. The book entered the Amazon list at number one, and a film deal brokered by producer and director Niall Johnson soon followed.
Although nothing could match the raw reality of losing Kate, making the film has been an emotional experience for St John, the more so as many of Kate's friends volunteered to appear as extras.
"So many times I had to quietly sneak away from filming," he says. 'It was just too much to take."
In the intervening years St John and his sons have fulfilled many of Kate's wishes, although not yet all.
"One important one was to have the boys roller skate in a museum, hilariously something they always wanted to do," he says.
"To my astonishment the Natural History Museum happily agreed to close for a bit and let us do just that. That was one of the most fun.
"And there is one special one we are about to carry out. Many years ago I convinced Kate to qualify as a scuba diver, which she did. My intention was to whisk her off to the Great Blue Hole in Belize, one of the best diving sites in the world. We never did make it.
"But Kate being Kate, included it as somewhere she wanted me to take the boys and that is in the offing. She will be so pleased."
Although his love for Kate has never waned, today life is very different for Singe and the boys.
Mindful that one of Kate's hopes was that he find another woman to help provide a stable family for their sons, he has a new partner.
"We are a family again," he says.
"But Kate will be forever in our lives."