The most common and most likely answer to this crossword clue is the 8 letter word ESCHATON
I've seen this crossword clue in The Times
E
S
C
H
A
T
O
N
Buddy explains!
The straight part
We know that "last event" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case last event = eschaton.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 ESCHATON mean?
ESCHATON noun- The world during the posthistoric era of God's overt (apocalyptic) reign, immediately preceding the end of the world.