The most common and most likely answer to this crossword clue is the 12 letter word DISAPPOINTED
I've seen this crossword clue in The Daily Telegraph
D
I
S
A
P
P
O
I
N
T
E
D
More clues leading to the result DISAPPOINTED
- I stopped and I collapsed, downcast
- Upset girl’s been chosen
- Upset when Democrat is given job?
- Frustrated detectives given job
- Girl’s set to be let down
- Daughter’s chosen to be gutted
- Crestfallen as Democrat is elected
- Upset as given the sack, it’s implied?
- Sad Mr James, funny fellow, being stood up then engaged
- Not pleased, finding sharp bit in pie Dad’s cooked
Buddy explains!

The straight part
We know that "Crestfallen" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case crestfallen = disappointed.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 DISAPPOINTED mean?
DISAPPOINTED verb- To sadden or displease (someone) by underperforming, or by not delivering something promised or hoped for.
- To deprive (someone of something expected or hoped for).
- To fail to meet (an expectation); to fail to fulfil (a hope).
- To show (an opinion, belief, etc.) to be mistaken.
- To prevent (something planned or attempted).
- Defeated of expectations or hope; experiencing disappointment; let down.
- Expressing or indicating disappointment.