The Dutch left-back returned to his homeland in October with AZ Alkmaar, where he made his top-flight debut last month in a 2-2 draw at Utrecht, and now joins fellow Eredivisie side ADO Den Haag on loan until the end of 2020/21.
Castillo signed for Chelsea from Ajax in the summer of 2016, having captained both the Amsterdam club and the Netherlands at youth level.
He helped our Academy win the Under-18 Premier League and FA Youth Cup during his first year with the Blues, which included completing the scoring in our 9-2 thrashing of Tottenham in the latter competition.
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