C&C: Red Alert

The final cutscene of the Soviet campaign reveals that Josef Stalin's then-unnamed advisor (played by Joseph D. Kucan) is actually Kane himself and that the Brotherhood of Nod have been manipulating the USSR into instigating World War II for their own interests, making Command & Conquer: Red Alert a prequel to Command & Conquer: Tiberian Dawn.

Example of:
Piggybacking on Hitler