Ten days have passed since Sarah Stevenson buried her mother and, on her first morning back at training, the taekwondo world champion needs to talk rather than fight. She also lost her father to cancer, just as shockingly, this summer. And so, after a brutal year, the 28-year-old sits in a bare lobby at a sports centre in Manchester and speaks with honesty as touching as it is searing.

"It's hard being back," Stevenson says on a hushed November morning. Yet she is unflinching in the way she refuses to look away or fiddle with the peeling upholstery as a means of hiding her feelings. "You get nervous. One: you forget what it's like being here. Two: the others are training for an Olympic test event that I won't be ready for [in London this weekend]. But the third reason is the main one why it's so hard."

Stevenson searches for the right words. "Sometimes," she eventually says, "people don't know what to say to you. I noticed it the first day I came back after my dad died. No one spoke to me and I felt like I'd done something wrong. They don't know what to say but they should just admit it. That would be enough for me. But I guess they need courage to come over and put their arm around you. People find it tough to talk."

It's actually easy to talk to Stevenson. In similar fashion, it's relatively simple to understand how she managed to win her world welterweight title in May, just two weeks after discovering that both her parents were suffering from terminal cancer. It only seems difficult to accept that one person should suffer so much in a single year. 2010 was different. She became European champion again and got married, last November, at a blissful wedding in Mexico. As a young wife and prospective Olympic gold medallist at London 2012, how did Stevenson and her husband, Steve Jennings, who is also her coach, feel when they looked ahead on their first New Year's Eve as a married couple?

"We felt great," she exclaims, her face opening up with the sweetness of a memory from a different life. "Last New Year's Eve, Steve and I went to this really posh do in Liverpool. It was all la-di-dah. That's not really me ..."

Stevenson laughs. "I got to put on a posh frock and really enjoyed it. But, yeah, it was all downhill after that."

Her laugh, this time, is raw rather than wry. In January, while Stevenson was with the British taekwondo squad in Cuba, her father called. "My parents were never ill and so it was a shock when dad said, 'Your mum's poorly but don't panic. It's just pneumonia.' But when I got home and saw mum I could tell they weren't really telling the truth. When she saw me, mum cried. And I'll tell you something that I've not told anyone outside my family. She didn't know she had cancer then but she was scared to go to hospital. She looked at me and said: 'I don't want to die'. For a daughter to hear them words..."

Stevenson shudders. "From that day I became her mum and looked after her. Dad was a proud man but he didn't know what to do with himself. They'd been married 40 years. That's a long time, innit? The day after we got told about mum I saw him downstairs and I just went and hugged him. He was so upset."

Diana Stevenson was given extreme doses of chemotherapy and her daughter was told that, if she could survive the ravaging treatment, recovery might be possible. But hope for her mum was soon darkened by her father's fate. "My cousin called [in April] and said: 'Your dad's been rushed [from Doncaster] to Sheffield," Stevenson remembers. "I raced over to Sheffield and dad looked horrendous. He had a cyst on the brain. They showed the scan to me and it was pretty big. But we had to wait for the results. At that time dad was on N floor of the hospital and mum was on P floor. I was going up and down. One day I sat in the waiting room, thinking: 'This can't be happening.'

"I said to my husband, 'My dad's got a brain tumour', and he said, 'Don't be stupid.' He was trying to keep me calm. But we got the results and it was an aggressive brain tumour. I had to go upstairs to tell my mum. I don't know how I did that ..."

Briefly, Stevenson looks utterly bereft. But her face refuses to crumple as she relieves those excruciating moments. "I had to pull the curtain round mum's bed to tell her. She knew dad was having these tests but she was devastated after I told her. She cried and cried."

Two weeks later, Stevenson found herself on a flight to Korea. Her parents might have been terminally ill but they insisted she took a break from caring for them and fought for the world championship. Stevenson finally accepted that her cousin would assume her role while she was in Korea. "At first I thought I don't care about the worlds. I'm going to fight a few random girls? What's that compared to everything at home? It's nothing. They can't hurt me. So I felt so much stronger, mentally, even though things were bad. It motivated me – rather than brought me down."

Stevenson smiles at her fighting mentality. "My husband knew I was on fire. I wanted to fight everyone. A couple of times, against the girls who weren't as good as me, I took it out a bit on them. But against the ones I really needed to focus on it was proper taekwondo. It wasn't about letting the anger out. I did what I needed to do to win. But I had that extra fire."

In the final, against Guo Yunfei of China, the contest was so tight that, even after the cruelly-named sudden-death decider, the scores were level. But Stevenson had been more aggressive and controlled throughout and the referee, after an agonising wait, rightly pointed to her as the victor. "I just let go," Stevenson says. "I couldn't stop crying. It was so intense. I hadn't been able to cry because I'd had to do so much at home. We were doing everything we could to stop mum and dad from dying."

Stevenson and her husband, who also coached two other British fighters to medals in Korea, went home to see her parents in Doncaster. They had both just been released from hospital. "They'd put all these flags up but I remember dad walked past me when I came in. I was thinking: 'Isn't he going to say hello?' But he'd run off to put on Cliff Richard's Congratulations on the CD. I could see he was different. He'd already changed in two weeks and it upset me. But the music started and the four of us were together."

Roy Stevenson died in July – two-and-a-half months after his tumour was diagnosed. And then, shortly afterwards, any lingering hope for his wife ended. "The word the doctors used was 'tricky'," Stevenson says, shrugging at the semantics surrounding terminal illness. "Her cancer was more 'tricky' than they'd expected. Until then they were convinced there'd be no cancer left after the chemo and I thought we'd have mum for a bit longer. But it turned out she still had cancer in her pelvis. I said 'How long?' They said 'A couple of months.' That was two weeks after dad's funeral."

Diana Stevenson died earlier this month. Her daughter looks up again. "She fought so hard and it was for nothing. It's such a savage disease and it gets you upset and angry. The day of her funeral was the worst of my life and I couldn't stop thinking that, exactly a year before, mum had been with me on my hen night in Mexico. Steve and I got married in Mexico and it meant the world to have my parents there with our friends. But my first wedding anniversary was three days after mum's funeral."

Stevenson has qualities that help her fend off bitterness and despair. "Even when she was ill we had some funny times. We took her to Skegness. The sun shone and it was good."

We sit on two small sofas, facing each other, and it's very quiet in a deserted building. All the cries and muted screams of sparring have faded as every other fighter has gone home. Most of them are consumed by the struggle to qualify for Britain's fast-rising Olympic taekwondo team. Stevenson, the star of the sport in this country and already an Olympic medallist, has guaranteed her place at her fourth Games.

But, having heard so many Olympians torture themselves over the prospect of competing or failing at London 2012, it's striking to listen to Stevenson – especially when considering her glaring omission from the men-only short-list for the BBC's Sports Personality of the Year. Stevenson deserves to be praised more than anyone else in British sport in 2011 but this world champion has a far more personal and significant battle to win.

"Since the worlds I've forgotten what it's been like to be an athlete," she says, "but at the same time I'm seeing 2012 logos everywhere. I think, 'God, I'd better get training again ...' But how can I really focus on that? I just want to get to January 2012 so I can leave 2011 behind. It's been a terrible year and you think: 'How the hell did that happen?'"

Stevenson holds my gaze. "I don't know the words, really. The only thing that comforts me is that mum and dad are together again. Well ... you hope they are. I hope more than ever that there's something after this."

What about her, Sarah, an ordinary young woman from Doncaster who has endured so much with extraordinary bravery and candour? "I've got to be an athlete now. I need to go to the Olympics. The first thing mum said when we knew it were cancer was: 'You've got to go to the Olympics and win it.' Same with dad. He just thought they'd be there to see me do it. He thought he was invincible. None of us are. But if I've got the same attitude I had at the worlds I know I can win the Olympics. I just want to have that fire I felt in Korea. I want to win gold for mum and dad. After that, I can start grieving properly."

Then, movingly, Stevenson reaches over to shake my hand. I thank her for talking so openly. "I enjoyed it," she says in surprise. As we prepare to walk out into the bright light of a winter morning, she laughs softly. "I guess talking like this is therapy. And maybe a few people might read this and think that, whatever's happened in their lives, it's worth going on. I'd like that."