The most common and most likely answer to this crossword clue is the 6 plus 1 plus 8 letter word MAKING A COMEBACK
I've seen this crossword clue in The Daily Telegraph
M
A
K
I
N
G
A
C
O
M
E
B
A
C
K
Buddy explains!
The straight part
We know that "Becoming popular again" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case becoming popular again = making a comeback.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.