The most common and most likely answer to this crossword clue is the 9 letter word PUNCHLINE
P
U
N
C
H
L
I
N
E
Buddy explains!

The straight part
We know that "end of joke" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case end of joke = punchline.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.
What does PUNCHLINE mean?
PUNCHLINE noun- The final part of a joke; the word, sentence, or exchange of sentences that is intended to be funny and provokes laughter from the listeners.
- More generally, a final, concluding statement that an explanation has been leading up to.