You may have difficulty without a written contract in this case (the fact that you have written contracts with others does not matter: this client is not bound by the agreements others entered into). Except where changed by a contract, content developed belongs to the *client*, not the designed or developer, as a "work made for hire"--when you are paid by someone to design or develop something, they own it, not you. While a contract can change that, so the creator keeps the rights, you state that you do not have a written contract; therefore, if litigation (i.e. a lawsuit) ensues, the client may be awarded ownership, based on what you write.