The most common and most likely answer to this crossword clue is the 8 plus 4 letter word FLIPPING NORA
I've seen this crossword clue in The Guardian
F
L
I
P
P
I
N
G
N
O
R
A
Buddy explains!
The straight part
We know that "by George!/by George!" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case by george!/by george! = flipping nora.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.