"Let's be proud of our national colours, let's be proud the we are Poles," Duda wrote.
A short film was also posted on the profile of the President's Office, showing Duda hoisting the national red-and-white flag, followed by the slogan, "Fly the flag!"
Since 2004, Flag Day has been celebrated in Poland on May 2, the feast day of the Polish Diaspora and Poles Abroad. (PAP)
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