The most common and most likely answer to this crossword clue is the 9 letter word MENTIONED
I've seen this crossword clue in The Daily Telegraph
M
E
N
T
I
O
N
E
D
Buddy explains!

The straight part
We know that "Declared" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case declared = mentioned.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 MENTIONED mean?
MENTIONED verb- To make a short reference to something.
- To utter a word or expression in order to refer to the expression itself, as opposed to its usual referent.