This is a reversal clue - look for indicators like 'back', 'returned', 'up' (in down clues), or 'west' (in across clues)
Reverse the letters of a word from the clue
Answer: PRIAPIC | Definition: 'Chap so excited' | Wordplay: An envelope (‘in’) of RIAP, a reversal (‘make comeback’) of PAIR (‘couple’) in PIC (‘film’). I think that Anto can be forgiven the adjectival answer (with extended definition?).