Apparently Harry Potter wasn't the only one who ever took issue with Professor Severus Snape.

Late actor Alan Rickman, who played the potions and defense against the dark arts teacher in the "Harry Potter" films, admitted in newly released letters that he had some "frustrations" with the character over the years.

Rickman, who died on Jan. 14, 2016, at the age of 69 after battling with cancer, kept piles of fan mail, journals, letters with co-stars and other items inside his home. The personal notes — enough to fill up dozens of boxes — are going up for auction at the ABA Rare Book Fair in London.

In one letter, film producer David Heyman thanked Rickman for making "Harry Potter and the Chamber of Secrets" a success.

“I know, at times, you are frustrated but please know that you are an integral part of the films. And you are brilliant," the note read, according to The Independent.

While filming "Harry Potter and the Half-Blood Prince" in 2009, Rickman criticized director David Yates in a letter titled “Inside Snape’s Head."

“It’s as if David Yates has decided that this is not important in the scheme of things i.e. teen audience appeal,” he reportedly wrote, though it's unclear what he's referring to.

High-profile celebrities such as J.K. Rowling, Emma Thompson, Daniel Radcliffe and Sting are among those featured in Rickman's impressive collection, The Mirror reports.

“It's a fabulous collection," actor and collector Neil Pearson told the British newspaper. "Every single script of a play or film, all of his diaries and a massive amount of correspondence from pretty much every one you’ve ever heard of.”