BIL had an aunt. She had no children but was the widow of a man with one son. The son had never lived permanently with them, but she'd been his step mum since childhood.
She lived to very old age and was an "old lady" for c. 20 years, in that she stopped driving, was confused about finances and anything "modern", needed (wanted?) a lot of help. In her last years she had dementia
She was never a particularly pleasant person and that got worse as she got older. She was wealthy and generous at birthdays and Christmas.
Anyway, BIL did loads for her, had POA and basically ran her finances, lots of DIY, taxi service etc. She could be very demanding and unpleasant if anyone said no to her, often using "the will". Step son saw her rarely after his father died.
BIL always said he wasn't doing it for the inheritance, just becuase there was no one else, but she had always led him to believe her estate would be split 50/50 between Step son and BIL (her nephew).
In the end, she left most to the step son with small legacies to BIL and some other relatives in her husband's side.
In some ways, she's done the right thing, she's passed her husband's estate (but also hers) to his son, but BIL is right to feel a bit miffed after all he did for her?