I'm curious about the role authorial authority has played in the past, especially what the authors themselves believed it to be. Therefore I'm looking for the earliest example of a work meeting the following conditions:

• A work of fiction based on another (original) work of fiction, namely something set in the same universe or using the same characters
• Both created around the same time, preferably with the derivative being published within the original author's lifetime (this would be hard to know for some older works)
• The derivative was not authorized by the original author (as was the case with Oz, for example)
• Could be any type of creative derivative, such as a prequel (but no translations)

Even before the internet, the twentieth century had many such works in spite of copyright. Even before that there were a few examples (as per Wikipedia).

The earliest I know of is of Don Quixote:

In 1614 a fake second part was published by a mysterious author under the pen name Avellaneda. This author was never satisfactorily identified. This rushed Cervantes into writing and publishing a genuine second part in 1615, which was a year before his own death.

Though Cervantes had no copyright law backing him, he still defended his "universe" as something uniquely his. The fact that an unauthorized sequel could be published at all must have been facilitated by the printing press, but is there anything earlier than that?

Can you beat 1605/1614 for the date of such a work?