You met Adar in the woods after escaping the Uruks and Annatar (Sauron). I stayed for a little bit waiting for him to come, about to leave until you see him with your ring (the white diamond silver one that he took). He gave it to you and looked at you genuinely.

"Lets make peace together"

You put the ring on and he notices Uruks of his come with his favourite son on a stretcher. He goes over and talks with him, words you didn't understand or hear until you see him get stabbed and then attacked by all the other Uruks that came; seeing Annatar stand in a distance watching with the crown in his hands wanting to give him the same death Adar did to him.