Clive admits wild rose from The Secret Garden, for instance, raised by his twin (5,8)
I believe the answer is:
close relative
'instance raised by his twin' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.
'clive admits wild rose from the secret garden' is the wordplay.
'admits' means one lot of letters goes inside another.
'wild' indicates an anagram.
'from' says to put letters next to each other.
'the secret garden' becomes 'elat' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'rose' is an anagram of 'oser'.
'oser'+'elat'='oserelat'
'clive' placed around 'oserelat' is 'CLOSE RELATIVE'.
'for' acts as a link.
Can you help me to learn more?
(Another definition for close relative that I've seen is " Auntie maybe".)