It was among documents being auctioned at Ludlow Racecourse, Shropshire, by Robert Marrington, ex-superintendent of works at Sandringham House, Norfolk.

Charles says of the 1988 avalanche at Klosters: "I find it hard to understand why I survived and he didn't."

The letter had a guide price of between �250 and �350.

Off-piste skiing

The 1988 avalanche killed Major Lindsay, a former Queen's equerry, and badly injured the mother of socialite Tara Palmer-Tomkinson, Patti, as the pair skied off-piste with Charles and his guide Bruno Sprecher.

Document specialist Richard Westwood-Brookes, of auctioneers Mullock Madeley, said other royal ephemera such as original tickets to the Queen's wedding in 1947 sold well.

A series of letters written by composer Sir Edward Elgar, including one concerning the copyright of his most famous work, The Dream of Gerontius, sold for a total of �2,300.