Could it be...Marie Antoinette?
In the category Ghoulish Greats for 300 points...In The Omen, David Warner plays Keith Jennings, a photographer/reporter who helps Robert Thorn (Gregory Peck), unravel the mystery of Thorn's child. As they get close to the evidence, Jennings meets his demise by being decapitated. What is the object that severs his head from his body?
Pane of glass!"b-dong, b-dong, b-dong, b-dong..." is the sound I imagine it was making... The 80s for 500And damn if I didn't think of Joan of Arc and dismissed it.