Hello!
It's possible that there isn't much behind this boss, since he was added in game around 2008 (1), and the place where he spawns, the Alatar's Lake, has been around since 1999 at least - since Loria, Alatar's apprentice, has been in game since 1999 (2). However, in the same place was added another NPC, called simply "A frog" (3), or Turian, added in july 2009, whose background story is about his short lived carreer as Eclesius' apprentice (4), where he accidentaly was transformed into a frog.
It seems that human-transformed frogs are relatively common in Alatar's Lake region, even though it is not possible to draw a conclusion, it is curious that Alatar's fate, or whereabouts, is not easily found anywhere - while, at the same time, the lake was named after him. So perhaps could the frog prince be Alatar himself, even if added much later than the original lake?
(1) https://tibia.fandom.com/wiki/The_Frog_Prince
(2) https://tibia.fandom.com/wiki/Loria
(3) https://tibia.fandom.com/wiki/A_Frog
(4) https://tibiasecrets.com/transcript.php?nm=A-Frog
Might also be of interest:
https://tibia.fandom.com/wiki/Samael
https://tibia.fandom.com/wiki/A_Confused_Frog