Prince of Thralls

• WWizards of the Coast2008-10-01
  Official Ruling
  If the permanent that caused the ability to trigger leaves the graveyard before the ability resolves (because it’s a token and it ceased to exist, or because a spell or ability removed it from the graveyard), the ability will still resolve. The opponent will have the option to pay 3 life. But whether or not that player pays the life, nothing will be returned to the battlefield.
• WWizards of the Coast2008-10-01
  Official Ruling
  If the ability triggers and your opponent chooses not to pay 3 life, you must return the card to the battlefield, even if you don’t want to.
• WWizards of the Coast2008-10-01
  Official Ruling
  It doesn’t matter whose graveyard the permanent is put into as long as an opponent controlled it when it last existed on the battlefield.

Rulings via Scryfall