A queen’s husband whose twins were healthy (8)

I believe the answer is:

bothwell

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'a queen's husband whose twins' is the definition.
I know nothing about this answer so I can't tell whether this works.

'were healthy' is the wordplay.
'were' becomes 'both' (I can't explain this - if you can you should give a lot more credence to this answer).
'healthy' becomes 'well' (similar in meaning).
'both'+'well'='BOTHWELL'

Can you help me to learn more?

(Another definition for bothwell that I've seen is " Royal husband".)

I've seen this clue in the Evening Standard.

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