The most common and most likely answer to this crossword clue is the 9 letter word UNEARTHLY
I've seen this crossword clue in The Daily Telegraph
U
N
E
A
R
T
H
L
Y
Buddy explains!

The straight part
We know that "It’s strange" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it’s strange = unearthly.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 UNEARTHLY mean?
UNEARTHLY adjective- Not of the earth; non-terrestrial.
- Preternatural or supernatural.
- Strange, enigmatic, or mysterious.
- Ideal beyond the mundane.
- Ridiculous, ludicrous, or outrageous.