Last working with artist of the stars (6)
I believe the answer is:
astral
'of the stars' is the definition.
(relating to stars or astronomy)
'last working with artist' is the wordplay.
'working' indicates anagramming the letters.
'with' means one lot of letters goes inside another.
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'last' is an anagram of 'astl'.
'astl' going around 'ra' is 'ASTRAL'.
(Other definitions for astral that I've seen before include "Altars (anag)" , "Resembling the stars - of the spirit world" , "To do with stars on altars" , "Starry sort of altars." , "Relating to stars" .)