Robert Lewandowski's grandfather was Bogdan Lewandowski, a Polish soldier who fought against the Nazis during World War II and passed away in 1989. There is a false rumor that Lewandowski is related to Adolf Hitler via Hitler's sister Paula Hitler, but this claim is baseless and has no factual support—Paula Hitler never had children.
Lewandowski's family is ethnically Polish, and he has no connection to Hitler. The misinformation likely originated as an internet joke or trolling. Lewandowski himself has condemned racism and discrimination and does not associate with such ideologies.
In short, Robert Lewandowski's grandfather was Bogdan Lewandowski, a Polish war veteran, not related to Adolf Hitler or his family.