The story of Arthur has been told and retold in hundreds of ways over hundreds of years, from Geoffrey of Monmouth's History of the Kings of Britain (c. 1138), the works of the late-twelfth-century French poet Chrétien de Troyes, and Sir Thomas Malory's Le Morte d'Arthur, to T.H. White's The Once and Future King, Rosemary Sutcliff's Sword at Sunset, and Bernard Cornwell's Warlord Chronicles.

The screen, too, has burned brightly with Arthuriana, from the 1963 movie The Sword and the Stone, to John Boorman's 1981 fantasy film Excalibur, and Guy Ritchie's 2017 movie King Arthur: Legend of the Sword. And of course one can't not mention Monty Python and the Holy Grail.

Yet throughout all the adaptations of the myth, we've seen little of Arthur's greatest knight and closest friend, the man whose tragic love affair with Arthur's wife Guinevere presaged the downfall of a kingdom. We've all heard of Lancelot, and of that most celebrated love-triangle in European literature, but many of us don't know much more than that. In literary terms, we might call Lancelot an under-developed, even flat character. The editorial note might say: 'This character could benefit from some fleshing out.'

There is a feeling that it is during the darkest times that we turn to our most luminous legends

I thought, wouldn't it be something to find out who Lancelot is, to get inside his skin and rewrite his story for today? I started writing the book in 2016, but then, just as I was finding my feet, my father fell suddenly ill. After several brutal weeks, and unimaginably, given his energy, determination and personal charisma, he died just two days before his seventieth birthday. He was gone. My world fractured and in the black shadow of shock and grief, I questioned everything. How trivial, even frivolous, to sit here making up stories in the midst of death and loss. How could I think that what I was doing was worthwhile? How did it make sense to be sitting here at my desk making stuff up while my heart was breaking?

And yet, some other part of me asked, in a guilty whisper, why do we write and read stories, if not to escape the mundane realities and torments of our lives? For a while I did not hear this small voice, and the writing was hard. During that time, the last place I wanted to be physically was stuck in a room on my own. Mentally, the last place I wanted to be was hanging out inside my own head, writing what is in essence a tragedy. I even began to question the point of writing books at all if my father wasn't around to be proud of me. It was a precarious time for me.

But writing is my job, and my publisher had signed up Lancelot, and, well, what else was I going to do? And so, I set my mind to doing the best I could. Still, whatever story I had originally set out to tell, it transmuted into . . . something else. It became less a story of events, of heroic deeds and familiar Arthurian tropes, and more a tale of love and loss, of all that might have been, and of a sense of time and place which stays with a person their whole life.

There is a feeling, I think, that it is during the darkest times that we turn to our most luminous legends. Who amongst us is not beguiled by Malory's romantic notion of Arthur as the 'once and future king'? Which of us will admit to never having entertained the childish yet thrilling hope that perhaps Arthur is not dead at all but simply waiting, and that in the hour of our direst need he will return to Britain to lead us through the struggle? It is, after all, a comforting idea, no less so in these days of global insecurity than in the tenuous times of the past. But then there comes a moment in our lives when the truth hits us, like a cold blade in the heart. Arthur will not come again. Loss and time will ravage hope, and the light in the darkness will inexorably fade. Through Lancelot, and not Arthur, I was able to explore this sense of the inevitable, and the idea that when all is said and done, we only have the promises we make, the courage we can muster, and the love that endures between us in spite of it all. Lancelot, in all the myths but not least in my version, is Arthur's greatest and best. And yet it will not be enough. It can never be enough.

This book is, then, in every sense a reimagining. For me it was a journey of spirit and memory, of imagination and of the senses. Perhaps Arthurian scholars will frown at the liberties that I have taken with the story. They may well disapprove of the diversions I've taken from Chrétien de Troyes, Malory et al. But I make no apologies. In life nothing stays the same, no matter how much we might want it to, and I believe legends must change too. They must adapt to the times and find new resonance. And if we dare to retell those legends from the heart, perhaps we help to keep them alive long after we are gone.