Be first, perhaps, to last the person one can most depend on (4,6)

I believe the answer is:

best friend

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'person one can most depend on' is the definition.
I can't tell whether this defines the answer.

'be first perhaps to last' is the wordplay.
'perhaps' indicates anagramming the letters.
'to last' becomes 'end' (I've seen this in another clue).
'first' anagrammed gives 'stfri'.
'be'+'stfri'+'end'='BEST FRIEND'

'the' acts as a link.

Can you help me to learn more?

(Other definitions for best friend that I've seen before include "Bosom companion" , "Mate" .)

I've seen this clue in the Evening Standard.

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