The most common and most likely answer to this crossword clue is the 7 plus 6 letter word BEATRIX POTTER
I've seen this crossword clue in The Guardian
B
E
A
T
R
I
X
P
O
T
T
E
R
More clues leading to the result BEATRIX POTTER
Buddy explains!

The straight part
We know that "Writer, illustrator" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case writer, illustrator = beatrix potter.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.