Heathcliff and the Catillac Cats

Grandpa vs. Grandpa [Heathcliff] (1x115)

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Iggy and Heathcliff are watching TV and see on the news that a prisoner escaped who looks just like Grandpa. When Grandpa comes home, they think it's him and try to hide him. The real prisoner shows up and Heathcliff and Iggy have to figure out which one is the real Grandpa.