Whose

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Old English hwæs, genitive of hwā ‘who’ and hwæt ‘what’.

wiktionary

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From Middle English whos, from Old English hwæs, from Proto-Germanic *hwes, genitive case of *hwaz(“who”) *hwat(“what”).

etymonline

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whose (pron.)

genitive of who; from Old English hwæs, genitive of hwa "who," from PIE root *kwo-, stem of relative and interrogative pronouns.