From Wiktionary: Pronunciation, (UK) IPA(key): /ˈskwɪ.ɹəld/, /skwɜːld/
Squirrelled has the longest spelling (11 letters) of any standard English word with one syllable. This spelling is not typically used in North America, where squirreled (10 letters) is used instead. Neither word is universally one syllable, as many accents pronounce it with two syllables.