Alloy needs refining? That's true (5)

I believe the answer is:

loyal

I'm a little stuck... Click here to teach me more about this clue!

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

'alloy needs refining?' is the wordplay.
'alloy' anagrams to 'LOYAL'.
However, I'm not clear how this is indicated.

'that's' is the link.

Can you help me to learn more?

(Other definitions for loyal that I've seen before include "Trusty" , "Steadfast and true" , "Faithful - true" , "Faithful (in allegiance)" , "Steadfast in allegiance" .)

I've seen this clue in The Daily Mail.

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