The most common and most likely answer to this crossword clue is the 6 letter word MURPHY
I've seen this crossword clue in The Sunday Telegraph
M
U
R
P
H
Y
Buddy explains!

The straight part
We know that "King Edward, say" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case king edward, say = murphy.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 MURPHY mean?
MURPHY noun- An Irish or white potato.