The most common and most likely answer to this crossword clue is the 3 plus 2 plus 5 plus 1 plus 2 letter word END OF STORY - DD
I've seen this crossword clue in The Times
E
N
D
O
F
S
T
O
R
Y
-
D
D
Buddy explains!
The straight part
We know that "Perhaps the final part in a history/period" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case perhaps the final part in a history/period = end of story - dd.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.