The most common and most likely answer to this crossword clue is the 9 letter word APPRISING
I've seen this crossword clue in The Times
A
P
P
R
I
S
I
N
G
Buddy explains!

The straight part
We know that "telling" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case telling = apprising.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 APPRISING mean?
APPRISING verb- To notify, or to make aware; to inform.
- The appraisal of the value of goods, land, etc., often in order to pay the debts of a deceased person.