My mother in law and I have a really tempestuous relationship. She recently waited until DP had left the room, and then said "Now G has left, I am going to say something' I told her she could say what she liked, I would tell him anyway. She then went on to say that she had heard I had said something about her pretending to be ill as an excuse not to attend DS 1st birthday party. I denied this (as I hadn't said it), and asked her to name the person she said had told her. She refused to do so, but said that if she heard me saying anything about her again, she would not come to our wedding in May 2014. I told her if I had anything to say, I would say it to her face, and if she didn't come to the wedding over something as trivial as that, her only sons wedding, then that was her issue, and she was being ridiculous, but really it was DP she would be upsetting, and not me. I don't think she was expecting me to say that, and she went quiet for a minute, then told me it was best if we didn't trouble DP with this conversation. I told her I would tell him anyway. Then DP came back and we carried on as normal. I did tell DP later on the drive home, and he was bemused by it.