I think you may be a little confused. The Black Knight could be several figures, most commonly it refers to Sir Ralph de Ashton (fl. 1421-1486) who served under Edward IV. As far as I know he has no connection with Kent. The Black Prince (aka Edward of Woodstock, 15 June 1330-8 June 1376), on the other hand, was the eldest son of Edward III and heir apparent. He is buried in Canterbury Cathedral.
The image though has nothing to do with either the Black Prince or Canterbury.