One of the other events I attended during the West Cork Literary festival was a talk by Nicci Gerard and Sean French who together are the crime/thriller/mystery writer Nicci French. It was fascinating to learn how they do what they do - and how Nicci French is almost a third person in their writing relationship. Their writing process involves a lot of trust in each other - one of them writes a chapter then emails it on to the other. The other has free rein to do with their work what they will - and then proceeds to write the second chapter. And so it goes on.
You would be hard put to identify which person has written which chapter - probably because they have both become so used to writing as Nicci French, rather than as themselves. Each one of them continues to write independently.
They must have enjoyed thinking up the title of this particular book!