Dependant on Hawking radiation. The best guess placed on the best guess, placed on the best guess. Doesn’t instill a lot of confidence here.
Hawking himself isn’t completely sure of his theory , but it’s also based on things that have since been proven to exist in laboratories, such as vacuum energy. Namely by way of the Casimir effect. Proving Hawking radiation, however, would be a lot more difficult; beyond our means in fact. It does make sense, however, they way I understand it.