Does it have to be the last straw? I'm not so sure. There are people who are determined not to like their child's partner from the beginning. I think that was my mil but eventually I won her round and I am sure she was jealous that I was taking her baby away. There are also insecure people who won't accept their partner's family, not because they did anything wrong but because they feel the need to 'own' their partner. Their are innocent people who get cut out.
Last weekend, in Rutland, the first statue in Britain of the late Elizabeth II was unveiled.