Fellow said to be serious (6)

I believe the answer is:

ernest

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'fellow' is the definition.
(I've seen this before)

I can't explain the remainder of the clue.

(Other definitions for ernest that I've seen before include "Name (of dramatic importance!)" , "fellow" , "Male" , "Resent (anag) - man" , "Boy's name (the important one!)" .)

I've seen this clue in The Mirror.

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