Crossword Genius

Nat King Cole song that will always be remembered? (13)

Ross

I believe the answer is:

unforgettable

I'm a little stuck... Click here to teach me more about this clue!

'remembered?' is the definition.
Both the definition and answer are adjectives. Perhaps they are linked in a way I don't understand?

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for unforgettable that I've seen before include "Always remaining in the mind" , "Striking" , "Highly memorable" , "Nat King Cole's memorable song?" , "stuck in my brain?" .)

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