double-cross

An act or instance of deliberate betrayal or deceit, especially in which one party violates a prior agreement or trust with a collaborator.

Of a breeding, the hybrid product of double-crossing.

To betray or go back on; to deceive someone after having gained their trust and led them to believe that they were being aided.

Of breeding, to cross twice in hybridization, as (A × B) × (C × D); for example, in commercial hybrid seed corn, A through D are classically inbreds, and their grandoffspring is the seed for sale.