Romantic gift went up Charles's backside (5)
I believe the answer is:
roses
'romantic gift' is the definition.
(I've seen this in another clue)
'went up charles's backside' is the wordplay.
'went up' becomes 'rose' (I've seen this in other clues).
'backside' says to take the final letters (the letter at the back).
The final letter of 'charless' is 's'.
'rose'+'s'='ROSES'
(Other definitions for roses that I've seen before include "the wars" , "Popular flowers" , "Bloomers" , "Red, white war symbols" , "Fragrant flowers" .)