Slave Collar. . . unimaginable rage. . .

[calmon]

curtadams said:
Note - even if you accidentally put a cursed item on a commander you can just restart the turn. It's not irreversable, you just lose the work you've done so far on that turn.

But not in this case. He wrote that his commander died in combat and his pretender get the item automatically. So this happens before the start of his next turn.