The most common and most likely answer to this crossword clue is the 8 plus 3 plus 7 letter word ETHELRED THE UNREADY
E
T
H
E
L
R
E
D
T
H
E
U
N
R
E
A
D
Y
Buddy explains!
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.