About a week before Game of Thrones season 5 launched, the first four episodes leaked.
Siddig spoke unusually candidly for a Game of Thrones actor, but then again, the show did massively underuse him and then promptly kill him off.
I am almost positive that those four episodes were leaked by HBO themselves.
Most assumed they stemmed from a preview screener (HBO stopped issuing them to journalists for season 6), but Alexander Siddig (Doran Martell) has a different theory.