City of Olympus almost ruined prominent couple from Thebes (8)

I believe the answer is:

plymouth

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'city' is the definition.
(Plymouth is an English city)

I don't understand the rest of the clue.

(Other definitions for plymouth that I've seen before include "Port of which Sir Francis Drake was once mayor" , "where sailors found" , "Laughter my ploy (anag)" , "Mayflower departure, arrival port" , "Devon port city" .)

I've seen this clue in The Times.

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