I'm worried that a prequel has even been writtem, the previous 2 books have played heavily on flashbacks and I for one have thought it an extremely enjoyable method, a prequel sort of leads to the idea that he's not going to do that anymore
Look at his website - the man is a fruitcake (I loved his first two books and have now read and re-read them, so I don't mean to insult him unecessarily). I've BOUGHT this book at waterstones and am now losing all hope of actually owning it. On his website he discusses several new Gentleman Bastard books, but I doubt any of them will be written. He has also started another series about some femme fatale... google him, you'll see.