I've written a short story about a true historical incident which involves a very famous person in history. The incident is true as are the people involved in it. But the story is a fictional eyewitness narrative of that incident from a person who was not mentioned in it, but could have been one of the principal witnesses.
What genre does this story fall under?
It can't be Alternate History because the narrative mentions an incident which actually happened.
Could it be Historical? Could be termed as Biographical?