8:38 AM PT -- Kevin Boon, the director of the horror movie starring the sister of accused Idaho murderer Bryan Kohberger says she never mentioned her brother during filming ... and he was super surprised to find out the two were related.
Kevin joined us on "TMZ Live" and told us he didn't realize the family connection until he started being contacted by media outlets.
The director says the only thing he knew about Bryan's sister's personal life was that Amanda was from Pennsylvania ... which is where Bryan was arrested.
Kevin tells us Bryan's sister was a joy to work with ... and Bryan never came around the movie set, as far as he knows. He says he feels really bad for the Kohberger family, especially Amanda.
Bryan Kohberger is accused of committing a murder that has markings of a horror movie ... a movie in which his own sister starred.
Amanda Kohberger has a single movie credit ... "Two Days Back," shot in 2011. The premise -- a group of students who are viciously stabbed to death with knives and other weapons.
The Mont Alto Film Project
The group of "environmentally-conscious students" take a hike in the woods. Their mission is to catch people who are illegally foresting.
The murderer befriends the group of students and then begins the massacre.
The director,Kevin Boon, was shocked when he learned of the connection between Amanda and her brother ... "You're f***ing kidding me, her brother is that guy?" Boon told the New York Post. He had kind words for Amanda, saying she was "a lovely woman who was very nice. I liked her a lot."
As you know, Bryan Kohberger is accused of butchering 4 University of Idaho students to death as they slept in their beds.