There is a Dragon Behind Humny(1983)

Overview:

In one royal forest, where coal miner Patočka lives and works, the friendly dragon Mrak settles down. The king's lackeys come across him while hunting and, terrified, go to sell the news to the king. He is currently organizing his daughter Viola's birthday party. The hunters describe the dragon in terrifying colors, and so the king concludes that the dragon will, according to tradition, want the king's daughter. So he announces a reward for killing the dragon, but no one wants to fight him. The only one who applies is the princess's favorite, the lutenist Marian, but the king does not like him, so he throws him out. Her brother Jan wants to save the princess, but the king doesn't want to allow it...