Beat prince — one kept celebrating achievement (9)
I believe the answer is:
triumphal
'celebrating achievement' is the definition.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for triumphal that I've seen before include "Showing excessive exultation" , "Celebrating a success" , "Exulting in success" , "Scenting victory" , "characteristic of success" .)