Guillermo Márquez is Dora's adorable Little brother. He is a 1 year old baby who has a pretty twin sister named Isabella. He wears a blue shirt and a white diaper. He appeared in many episodes of Dora the Explorer starting with "Big Sister Dora". Like Isabella, he remained unnamed until the episode Dora's Jack-in-the-Box, where his name was revealed. Like Isabella, he appears in the Dora and Friends episode "Magic Land", in which he appears a little older and can speak in full sentences.
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Guillermo as seen in the kaleidoscope promo for Dora The Explorer.
