Darling princess is back; cool (5)
I believe the answer is:
tepid
'cool' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for tepid that I've seen before include "Warmish" , "lacking enthusiasm" , "without passion" , "Moderately warm" , "Slightly warm" .)