Arthuriana -- all things King Arthur ! discussion

Back in the 80s I read a book titled something similar to "The Secret of the Knoll". It was about a young boy with a physical disability. He was staying at something like a monastery. While there he discovers secret passages and possibly the burial place of King Arthur. By the end of the book he keeps the secret but has healed and can walk normally. Does anyone have more information about this book or the exact name. I want to locate it again. It was an old book at the time i read it. That is all I know. Thanks for any info you can provide!