It looks like TV Chosun makes their dramas available to everyone in the world via the link on their website. Or maybe they just forgot to close this link since they don’t produce a lot of dramas (they mostly focus on news). Either way, the live watch for Grand Prince is available!
HOW TO LIVE WATCH GRAND PRINCE
STEP 1: Go to TV Chosun’s homepage.
STEP 2: Click on “ON” Icon in the upper right
STEP 3: The live watch window should automatically pop up. This link also takes you directly there.
If it doesn’t pop up for you then perhaps this method will not work for you. But it looks like this is not country locked, so it could be something to do with your computer or browser. Grand Prince airs Saturday and Sunday at 22:50 Seoul time. We aftercap it right after Misty, on Saturday, and Livecap it on Sunday.
Source TV Chosun