“Please meet Mikhail Ivanavich Duda (on the left) and Andrzej Sebastian Duda (on the right). DUda on the right is the current President of Poland. Duda on the left is the president’s grandfather, Ukrainian nationalist and Stepan Bander’s friend”.
This fake was floating around the Internet back in 2015. Even then, Duda explained on his Twitter that he had nothing to do with the Ukrainian Mikhail Duda.
"A total bullshit. My grandfather Alojzy Duda lived in Stary Sącz, was a furrier and died on 1 July 1992," the Polish president wrote on his Twitter.
The biography of the Polish president also refutes it. In Polityka magazine, Duda himself and his father Jan spoke in detail about their roots. Their family came from the town of Stary Sącz, which is from Ukraine. Andrzej’s grandfather's name was Alojzy, grandmother’s name was Kinga and they had six children. Grandfather worked as a furrier in a labor cooperative, lived poorly, and the family was religious. There is even a photo of little Andrzej Duda with his grandfather Alojzy. He died in 1992.
As for the Ukrainian nationalist Mikhail Duda, Polish historian Grzegorz Motyka in his book "Ukrainian partisans 1942-1960" wrote that he committed suicide in 1950 after an encounter with Soviet spies. Andrzej Duda was not born until 1972, so there is no way they could have had a photograph together.