Stephen King has made a reference to Harry Potter in his latest novel 'Dark Tower' which is book number seven in the series.
Here is the segment where Potter is mentioned:
Quote:
"Check out the crate-lid," Jake said when they joined her.
Susannah had set it aside; Jake picked it up and was studying it with admiration. It showed the face of a smiling boy with a lightning-bolt scar on his forehead. He was wearing round glasses and brandishing what appeared to be a magician's wand at a floating sneetch. The words stenciled beneath the drawing read:
PROPERTY 449TH SQUADRON
24 "SNEETCHES"
HARRY POTTER MODEL
SERIAL #465-17-CC NDJKR
"Don't Mess with the 449!"
We'll Kick the "Slytherin" Out of You!
Harry Potter has also received mentions in other books such as Dan Brown's "Da Vinci Code" and book #5 in King's Dark Tower series.
Sources:
The Leaky Cauldron who provided the transcript &
Mugglenet.
Reference to Harry Potter in Stephen King's latest 'Dark Tower' 
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