He-Man and the Masters of the Universe (1983)

S1E63 The Once and Future Duke

While taking a leisurely break to fish, Adam and Cringer spot a young boy in danger of being devoured by a carnivorous plant. Transforming into He-Man and Battle Cat, they spring into action to save him. After the rescue, Adam and Teela realize the boy is David, a friend from their childhood, who hasn't aged a day. The Sorceress reveals that David’s wicked uncle, Count Marzo, cast a spell to revert him to childhood and erase his memories. To restore David, they must find the Ring of Remembrance hidden in the Lake of the Lost. However, as He-Man, Teela, and Battle Cat search for it, Count Marzo captures David once more, planning to harness his magical abilities to thwart their efforts.