Lack of impulse control and empathy

I had a situation today with my husband and I’m at a bit of a loss. He has MCI with some vascular breakdown affecting executive functioning. We had our 8 year old granddaughter over and she brought her soaker gun to play with Papa. In the first few minutes my husband shot her in the face with water while she was yelling … No Papa… over and over. I came out and she was sobbing while he was laughing. It took a few minutes to get him settled and to back off. It scared me and I’m not sure what to do if it happens again. Has anyone encountered something similar? He loves her to the moon and back. Help?