He sounds sincere (6)

I believe the answer is:

ernest

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

I cannot understand how the remainder of the clue works.

(Other definitions for ernest that I've seen before include "- Bevin, twentieth century Labour politician" , "- Shackleton, Antarctic explorer" , "- Hemingway, - Shackleton" , "The boy sounds serious" , "Author Hemmingway, and Oscar Wilde's hero" .)

I've seen this clue in the Evening Standard.

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