The most common and most likely answer to this crossword clue is the 1 plus 5 plus 2 plus 3 plus 4 letter word A STING IN THE TAIL
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More clues leading to the result A STING IN THE TAIL
Buddy explains!
The straight part
We know that "an unexpected disappointment at the end" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case an unexpected disappointment at the end = a sting in the tail.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.