Here's the official description of the dish from The Brown Hotel:
In 1923, The Brown Hotel drew over 1200 guests each evening for its dinner dance. In the wee hours of the morning, the guests would grow tired of dancing and retire to the restaurant for a bite to eat. Bored with the traditional ham & eggs, Chef Fred Schmidt delighted his guests by creating The Hot Brown - an open-face turkey sandwich with bacon, pimentos, and a delicate mornay sauce.
The Hot Brown was made in 1923
Here in Kentucky, not in Tennessee.
-The Hot Brown Cheer