Shape epic jests, all exposed as most joyous (8)

I believe the answer is:

happiest

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'most joyous' is the definition.
('happy' can be similar in meaning to 'joyous')

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for happiest that I've seen before include "Most gay" , "extremely contented" , "Most content" , "Gladdest" , "Most contented and satisfied" .)

I've seen this clue in The Telegraph.

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