The most common and most likely answer to this crossword clue is the 3 plus 2 plus 3 plus 4 letter word OUT OF THE BLUE
I've seen this crossword clue in The Daily Telegraph
O
U
T
O
F
T
H
E
B
L
U
E
More clues leading to the result OUT OF THE BLUE
- Without warning, released article about old female, depressed
- Appearing unexpectedly
- Unexpectedly excluded from the honour of representing Oxford or Cambridge
- Coming from the sea, unexpectedly
- Unexpectedly published, ring fellow livid about article
- Marine's from nowhere
- Marine from nowhere
- Wherefrom sunbeams descend without warning?
Buddy explains!
The straight part
We know that "Unexpectedly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unexpectedly = out of the blue.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.