The most common and most likely answer to this crossword clue is the 9 letter word DESOLATED
I've seen this crossword clue in Financial Times
D
E
S
O
L
A
T
E
D
Buddy explains!

The straight part
We know that "forlorn" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case forlorn = desolated.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 DESOLATED mean?
DESOLATED verb- To deprive of inhabitants.
- To devastate or lay waste somewhere.
- To abandon or forsake something.
- To make someone sad, forlorn and hopeless.