"I'd forgotten about that."

I asked Mom if she missed her mother. She went on to talk a little about Grandma. Dad, listening but not always able to respond, wondered who we were talking about. When Mom got really close to his face to say gently, "My mother passed away; did you know that?" He silently looked at her, and then, clearly and quickly, (and surprising all of us) he said, "I'd forgotten about that."