Blue-blooded boys (5)

I believe the answer is:

royal

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'blue' is the definition.
(royal blue is a kind of blue)

I don't understand the remainder of the clue.

(Other definitions for royal that I've seen before include "Like Priam" , "Member of monarchy" , "Excellent" , "Relating to a sovereign" , "- blue; - assent" .)

I've seen this clue in the Evening Standard.

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