The truth about a trainee (4)

I believe the answer is:

real

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'the truth' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

'about a trainee' is the wordplay.
'about' becomes 'rea' (I've seen this in other clues).
'a trainee' becomes 'l'.
'rea'+'l'='REAL'

Can you help me to learn more?

(Other definitions for real that I've seen before include "Existing, not imaginery" , "Actual, existing" , "Actual, not illusory" , "Lear, strangely, could actually exist" , "'Genuine, actual (4)'" .)

I've seen this clue in the Evening Standard.

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