The most common and most likely answer to this crossword clue is the 10 letter word PREVIOUSLY
I've seen this crossword clue in The Daily Telegraph
P
R
E
V
I
O
U
S
L
Y
More clues leading to the result PREVIOUSLY
Buddy explains!

The straight part
We know that "until now" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case until now = previously.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 PREVIOUSLY mean?
PREVIOUSLY adverb- (with present-tense constructions) First; beforehand, in advance.
- (with past-tense constructions) At an earlier time.