The most common and most likely answer to this crossword clue is the 8 letter word DECEMBRE
I've seen this crossword clue in Financial Times
D
E
C
E
M
B
R
E
Buddy explains!
The straight part
We know that "Last mont/h/ in 19" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case last mont/h/ in 19 = decembre.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.