Mentioning capital gains tax may not be the most helpful but it's one way to approach it
If HMRC find it wasn't sold at around market value there could be a fine involved.
That'd be spiteful though.
Just live with it, why are you bothered? I don't care about what help my sibling got from my parents, good for them, that's their business.
E: Maybe you mum has been 'lying'' for worrying about you losing your mind over it.
She's probably planning on giving you the house she's living in now.
Besides, it's her house, she can do what she wants with it.
I expect she didn't say anything because she knew how the conversation would go, I expect she's dreading the conversation as much as you are chief.
Indeed. Why is he so sure the conversation will go badly and why didn't his mother think she could be upfront with him?
These sort of family disputes make me sad. Does your sister need more help than you? Maybe you're in line for more, who knows?
Another key question. Why would his mother do this in the first place? Maybe there are good reasons why the sister needs or deserves some help. Isn't the mother allowed to do what she wants with her own property?
By all means have the conversation, but taking a calm and reasonable approach and actually listening to what your mother has to say before considering your response seems essential. If you go in all entitled and fired up then you may well live to regret it.