The most common and most likely answer to this crossword clue is the 5 plus 5 letter word SHELL SHOCK
I've seen this crossword clue in The Daily Telegraph
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More clues leading to the result SHELL SHOCK
Buddy explains!
The straight part
We know that "Disturbance after a past engagement" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case disturbance after a past engagement = shell shock.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 SHELL SHOCK mean?
SHELL SHOCK noun- A stunning shock.
- A psychiatric condition characterized by fatigue caused by battle.
- A person with the condition.
- To stun or debilitate as by a shock.