His mother knew something about it only after you told herthe truth.

His mother knew （nothing ）about it （until ） you told herthe truth.
如果不明白,请再问；如果对你有所帮助,
请点击本页面中的“选为满意回答”按钮,两个字“理由”根据原句的意思：他妈妈中有在你告诉她真相后才知道一些情况。换句话说就是：他妈妈什么都不知道直到你告诉她真相。