Key singers upset following lines using celebs only (3-4)
I believe the answer is:
all-star
'key singers upset' is the definition.
The definition suggests an adjective which matches the answer.
'lines using celebs only' is the wordplay.
I cannot really understand how this works, but
'lines' could be 'll' (l is an abbreviation for line) and 'll' is present in the answer.
The remaining letters 'astar' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'following' acts as a link.
Can you help me to learn more?
(Other definitions for all-star that I've seen before include "Comprising only top performers" , "(Of cast or team) made up entirely of the famous" , "Made up of outstanding performers only" , "Composed wholly of top performers" , "Entirely comprised of top players/actors" .)