The most common and most likely answer to this crossword clue is the 8 letter word SUDDENLY
I've seen this crossword clue in The Daily Telegraph
S
U
D
D
E
N
L
Y
More clues leading to the result SUDDENLY
- Without warning, secretive, underground hollow lair invaded
- Duly ends assembly without warning
- In South of France, study in front of library that’s been evacuated without warning
- Rocky dude — Sly — boxing third of contenders straight away
- Duly ends broadcast without warning
- Fiddle duly ends and from out of nowhere...
- Doctor duly ends totally unexpectedly
- Eccentric lady’s nude, dropping attire initially in two shakes
Buddy explains!

The straight part
We know that "in two shakes" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case in two shakes = suddenly.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 SUDDENLY mean?
SUDDENLY adverb- Happening quickly and with little or no warning; in a sudden manner.