What was the brief history given by the housekeeper regarding the blood-stain?

In Chapter One of "The Canterville Ghost," Mrs Otis, one of the new tenants of Canterville Chase, spots a "dull red stain" on the floor of the library. This prompts Mrs Umney, the housekeeper, to reveal that the stain is, in fact, human blood and that it was spilt under horrifying circumstances.
According to Mrs Umney, the stain dates back to 1575 when Lady Eleanore was murdered on "that very spot" by Sir Simon de Canterville, her husband. Mrs Umney does not reveal the motive for the murder, but she goes on to say that Sir Simon died nine years after his wife, in 1584, in "very mysterious circumstances" and that his body was never found.
Finally, because the stain cannot be removed, Mrs Umney notes that the blood-stain has become a very popular sight among tourists and visitors to the house and that the "guilty" spirit of Sir Simon still haunts Canterville Chase.