Anonymous lover is quite a card (9)

I believe the answer is:

valentine

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'card' is the definition.
(I know that Valentine is a type of greeting card)

I can't explain the rest of the clue.

(Other definitions for valentine that I've seen before include "Message for February 14" , "Love card" , "February patron saint of lovers" , "Potential lover" , "A loving greeting card sent on February 14th" .)

I've seen this clue in The Globe and Mail.

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