The most common and most likely answer to this crossword clue is the 7 plus 3 letter word JALEBIS (B)
J
A
L
E
B
I
S
(
B
)
Buddy explains!
The straight part
We know that "Keats after swarmer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case keats after swarmer = jalebis (b).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.