Princess supporting actor and new dramatist (8)
I believe the answer is:
sheridan
'dramatist' is the definition.
(I've seen this before)
'princess supporting actor and new' is the wordplay.
'princess' becomes 'ida' (Princess Ida is a Gilbert and Sullivan opera).
'supporting' says to put letters next to each other (in a down clue, some letters go below others).
'actor' becomes 'sher' (actor Antony Sher).
'and' means one lot of letters go next to another.
'new' becomes 'n'.
'ida' put after 'sher' is 'sherida'.
'sherida'+'n'='SHERIDAN'
(Other definitions for sheridan that I've seen before include "Creator of Mrs Malaprop in The Rivals" , "Irish writer" , "Richard Brinsley . . . . . . . . was a great 18th century Irish playwright" , "Who scandalised the educational establishment?" , "Irish playwright and politician, d. 1816" .)