This bit would have been such a lovely opportunity for some wholesome mother-son bonding via sweet, sweet regicide.
Don't you think?
Go on, you can be each other's alibi. I would normally recommend not having any witnesses to such deeds, but the odds that your mother or your son will decide to rat on you for the murder you did together are probably lower than average.
Sorry, did I say murder? Of course it wasn't murder. He just died. Look, there were two of them in the room, surely one of them would have noticed if the other had done something like that? What, don't you trust them? It's his wife and his son! He can't have been murdered by his wife and his son!