I knew Richard was going to die. He'd been in a road-traffic accident - his bike had collided with a lorry - and he was in a coma.

When I first saw him, in intensive care, I thought: "Oh my God. That's it." I went into deranged professional mode: it was my way of coping. I remember talking to the anaesthetist, saying, "You've got to nurse him at 30 degrees head-up. That will lessen the chance of cerebral oedema and raised intra-cranial pressure."

Our daughter, Alice, was 16 months old, but she knew something was wrong. She went round the house calling "Daddy!", trying to find him. Jack was three and a half. I took him to intensive care. While Richard was being ventilated, Jack sat by his bed, drawing pictures. I videoed it all so Jack could watch it later, if he wanted to.

I believe that Richard waited to see Jack, because he died the very next day. He'd been in intensive care for eight days, in the National Hospital for Neurology and Neurosurgery, around the corner from Great Ormond Street, where I work as a paediatric oncologist. From one of the stairwells at Great Ormond Street, you can look into the intensive care ward. Even now, I can't go down that stairwell.

Grief and grieving didn't play much part in the syllabus when I was at medical school. We had the odd seminar on how to deliver bad news, which led into some awful role-play. I learned nothing. But I've always felt quite sure of myself emotionally. I'm not afraid of crying with patients, and I can get them to talk to me.

As a paediatrician, I love the fact that children have no side to them. They either like you or they don't - you know where you are with them.

No matter how often you do it, telling a family the worst news they're ever going to hear is painful. It's the hardest part of the job. You see parents in the most awful situations. The grief has left them bare.

Inevitably, you relate to some people more than others because you glimpse yourself in them. You think, "This could be me." Since I lost Richard, that has happened more frequently. I have to make more effort to detach myself in order to help as much as I can. You can't equate the loss of a child with the loss of a spouse, but I do understand what the families are going through.

Before Richard died, I'd come home to my very-nice-thank-you home life and unpack the day a bit with him, as far as patient confidentiality would allow, and then I'd reach the point at which I could think, "Well, thank God it's not me," and switch off. You have to, or you'd go mad. After he died, I was off work for a year. When I did go back I would come home from the hospital absolutely exhausted, the children would be pleased to see me, we'd all get ready for bed together and invariably I'd fall asleep before they did. I used to wake up at 11pm, realising I hadn't eaten anything, I hadn't spoken to anyone. I was wrung out, completely drained.

My children were my sanctuary. The useful thing I'd learned from oncology was that you should always be honest with children: if you don't tell them the truth, they will invariably sense that and their imaginations will take off. They have as much right to grieve as adults do. Pretending everything is OK is wrong. Everything was not OK. Jack and Alice had lost their father. The worst thing in the world had happened to them and they had a right to be as sad as I was.

Some people were freaked out by the way I involved the children. Right at the beginning, when I talked about taking Jack into intensive care, some friends asked, "Are you sure?" People said they wondered whether I wasn't exposing him to unnecessary hurt - was it good for him seeing me cry all the time? I didn't know what I could do about that. And I didn't really care what anyone else thought. No one knew my children better than I did.

Jack came with me to the chapel of rest. He'd painted a picture of heaven and chosen some special objects - Richard's best paints and brushes - which he put in the coffin. I felt Alice was too young to come to the funeral, but Jack wasn't. As we all walked out after the service, behind the coffin, Jack chanted, "I'm following my daddy, I'm following my daddy."

I bought loads of children's storybooks that dealt with death. The most useful one was Alan Durant's Always and Forever, about a fox who is part of the family and who dies. Jack made me read it every single night for months. The last line is: "The father of the family, always and forever." Every night I'd have tears streaming down my face, but I knew somehow it was helping him. Then suddenly, one night, he chose a different book.

People are so frightened of the bereaved. I got used to acquaintances crossing the road when they saw me coming. Some people seemed to think that if they didn't mention Richard's death we could all pretend nothing had happened. I guess they were scared of saying the wrong thing, making the situation worse. But how could it be worse?

What was useful was people arriving on the doorstep with a casserole: "Gas mark six, half an hour." Sure, people would say, "Give me a ring if there's anything I can do." But I simply didn't have the resources to phone. It would have been such a slap in the face if they'd said no. I'd lost so much, I couldn't risk losing any more.

I never resented anyone crying in front of me. Quite the opposite. I felt consoled by it. I felt that they were sharing in my grief. You can't push grief from your mind. It's in every fibre of you, every corner of your brain, every waking minute. It's pointless and trivial and difficult to talk about anything else.

Some colleagues suggested, after I was widowed, that I should think about whether I wanted to continue in paediatric oncology. They must have been wondering if, in my shoes, they could do it. But I never considered a move. Everything about my life was different: work was one of the few bits of the landscape that looked familiar.

Gradually, kicking and screaming, we became a team of three, not four. That's when I realised we could do it. We could cope. At some point you have to live with what has happened.

Jack still talks about the happy things he did with his dad. He remembers how Richard used to take him to nursery, the walk down the hill, hand in hand. And he has this desire to be like Richard. Their similarities are a real source of pride for him. He makes a big thing out of liking huge cooked breakfasts, because Richard loved them. He wants to be an artist when he grows up, like his father. When I say, "Oh, you are stubborn, just like your dad was," he revels in it. He thinks that's fantastic.

Had Richard not died, I would have been with him for the rest of my life, and he is still with me - just not physically. Lots of men would go, "Right, I'm off then." But Adam is not threatened by Richard, because he has been through the same thing. His first wife, Deborah, had breast cancer, and he began his grieving many years before the physical loss.

Adam and I got engaged on January 13 2006, five weeks after we got together, and we got married on January 20 2007. I feel no guilt for being happy again. You can't compare the marriages, just as you can't compare Richard and Adam. What I had was amazing and perfect, and what I have is amazing and perfect, in a different way. On my second wedding day, in my speech, I said thanks to Deborah and Richard, because if it hadn't been perfect the first time, then we wouldn't be doing it again. I do view myself as very lucky, in some bizarre respect, because I've fallen in love with two unbelievably fantastic men. Some people never truly fall in love once.

Jack and Alice still talk about their "old daddy", but Adam is their new father. They're comfortable about compartmentalising it in that way. And I do believe it's because they dealt with Richard's death when it happened.

I used to have very set ideas of how people should grieve: the step-by-step process. Now I realise there is no right, no wrong. People grieve in very different ways, according to their personalities. I sometimes tell patients' parents what has happened to me. I think it can help, occasionally, to know that I understand loss.