In The Last Battle, the main characters of the series arrive in Narnia one last time, having died in a train wreck in England.
"There's not much to tell," said Peter. "Edmund and I were standing on the platform and we saw your train coming in. I remember thinking it was taking the bend far too fast. And I remember thinking how funny it was that our people were probably in the same train though Lucy didn't know about it-"
Aslan explains further:
"There was a real railway accident," said Aslan softly. "Your father and mother and all of you are—as you used to call it in the Shadowlands—dead. The term is over: the holidays have begun. The dream is ended: this is the morning."
It's fairly obvious that Lewis, who uses a lot of symbolism and metaphor in the series, wrote this to describe death in the physical world leading to the afterlife in heaven. But regarding the train wreck specifically: Did Lewis ever confirm the exact inspiration behind it, or comment on it at all?
In The A-Z of C.S. Lewis by Colin Duriez, the character's deaths are mentioned:
One of the strangest features of The Last Battle, in a twist reminiscent of Charles Williams, is that all the principal characters from our world who come into Narnia are already dead as a result of a train accident. There are some similarities with Lewis' The Great Divorce, in that events after death are imagined, and a vision of heaven is presented.
Charles Williams was a fellow writer and close friend of Lewis, but I don't know how the 'twist' ending is reminiscent of his work. Was the train wreck scene possibly inspired by Williams?
Did C.S. Lewis ever explain the scene, perhaps in journals or letters?