Shocking debts faced by, say, Sir Elton once (9)
I believe the answer is:
egregious
'shocking' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for egregious that I've seen before include "Flagrant; appalling" , "Outstandingly villainous" , "Intolerable" , "Outstandingly bad" , "Extraordinary" .)