Crossword Genius

Be first, perhaps, to last the person you can most rely on (4,6)

Ross

I believe the answer is:

best friend

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

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

'be first perhaps to last' is the wordplay.
'perhaps' is an anagram indicator.
'to last' becomes 'end' (I've seen this in another clue).
'first' with letters rearranged 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 "Mate" , "Bosom companion" .)

I've seen this clue in the Evening Standard.
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