Mel, the penguin, and Walrus were searching for the trident, and they run into a groups of seemingly nice kids/ mermaids.
The blonde one who said " hey guys meet Mel Mel". He looks like the same boy who asked Melody to dance at her party.
Were they two different people, or did the boy turn into a merman?
This is a wild (and quite frankly) stupid theory that has long since been disproved. Simply having blond hair does not make two people the same person. Yes, they did look somewhat similar, but there were a lot of things that separate the two (like their eye color, skin tone, and highlights in the merboy's hair). Disney has also rejected this theory.
It is widely believed that the merboy (who's name is Alex by the way), is the son of Urchin from the TV series. Disney has neither confirmed or denied this theory, but it's widely accepted to be true.
He's Tidus. It's a Final Fantasy X reference.
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