First gorilla in new sanctuary, finally (10)
I believe the answer is:
originally
'first' is the definition.
(I've seen this before)
'gorilla in new sanctuary finally' is the wordplay.
'new' indicates an anagram.
'finally' says to take the final letters.
The final letter of 'sanctuary' is 'y'.
'gorilla'+'in'='gorillain'
'gorillain' with letters rearranged gives 'originall'.
'originall'+'y'='ORIGINALLY'
(Other definitions for originally that I've seen before include "to begin with" , "At the start" , "In the first place" , "new way" .)