I trusted him, but he double-crossed me and kept the prize money for himself.

double-crossed 是动词 double-cross 的过去式。double-cross 由 double（双重的）和 cross（欺骗、背叛）组成，字面意思是"双重欺骗"，指"背叛、出卖"的行为，特别指违背对信任自己的人做出的承诺。