The most common and most likely answer to this crossword clue is the 7 plus 6 letter word ONE-HIT WONDER
I've seen this crossword clue in The Guardian
O
N
E
-
H
I
T
W
O
N
D
E
R
Buddy explains!
The straight part
We know that "Star briefly/Star briefly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case star briefly/star briefly = one-hit wonder.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.