Well, in a way.
Beren and Lúthien (Amazon link), a love story about a mortal man and an immortal elf, was edited by son Christopher and “contains versions of a tale that became part of The Silmarillion.”
Plus it has fantastic illustrations from Alan Lee. I just ordered it today!
This is particularly sweet: “The names Beren and Lúthien are carved on the gravestone Tolkien and his wife share in Wolvercote cemetery in Oxford.”