The 24-year-old instead opted to sign for Bundesliga outfit Hamburg, despite holding talks with Ajax technical director Martin van Geel.
Castelen told Sportweek magazine: "It is correct that Martin van Geel called my agent Rodger Linse in the summer. I felt that Ajax showed their guts then. Trying to get a Feyenoord player to sign at Ajax is something you don´t do very often."
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