I'm reading Mary Stewart's The Crystal Cave just now and happened to look at the acknowledgements page last night. Among those thanked by the author is Robin Denniston, who through the 1960s and early '70s was editorial director and managing director of Lady Stewart's publisher Hodder & Stoughton.
Robin, who died in 2012, was our next-door neighbour some years ago; he was a charming gentleman and an excellent pianist. Latterly he had been with Oxford University Press, and when we knew him he had given up publishing to become an Anglican priest, so I had no inkling then of his illustrious career at Hodder and it is only now that I have discovered his connection to Mary Stewart; had I known, I'd have asked him all about her, but this piece of his (which was published posthumously) does tell us a little.