Crossword Genius

Old king of Spain left in debt-ridden state (8)

Ross

I believe the answer is:

ethelred

'old king' is the definition.
(as in thelred the Unready, medieval king)

I cannot understand how the rest of the clue works.

(Other definitions for ethelred that I've seen before include "Early English king" , "Baleen used to stiffen corsets, etc" , "King nicknamed the Unready" , "Old king" , "English king between nine hundred and seventy-eight and ten hundred and sixteen" .)

I've seen this clue in The Guardian.
Want a hint initially instead of a full solution? Install my app