In *A Good Man Goes to War* we meet Lorna Bucket, who is from the Gamma Forest. Throughout the episode we learn that The Doctor had some sort of an adventure in the Gamma Forest the result of which was: 

1. The Gamma Forest became neutral.
2. Doctor came to mean a mighty warrior, in the language of the forest.

Does anyone know what happened there. Is it a story in any form (written, audiobook, comic) ?