Crossword Genius

Disloyal unit I have left with regret (6)

Ross

I believe the answer is:

untrue

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

'disloyal' is the definition.
(similar in meaning)

'unit i have left with regret' is the wordplay.
I cannot quite understand how this works, but
'unit' could be 't' (T is an example) and 't' is located in the answer.
'regret' could be 'rue' (to rue something is to regret it) and 'rue' is found in the answer.
The remaining letters 'un' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for untrue that I've seen before include "Inexact" , "Not accurate or veracious" , "like the magnetic north?" , "Not level" , "Not loyal" .)

I've seen this clue in The Globe and Mail.
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