Why Katy Perry Can't EVER Forgive Russell Brand

Russell Brand is entering Justin Timberlake territory at Us Weekly apparently.

No matter how little evidence they may have, they're convinced Russell is a bad dude. Whenever Katy Perry gets around to writing material for her third album, the tabloid erroneously claims, she's got plenty of dark, painful memories to draw from!

The reason for that? Russell is (allegedly) penning a book about her!

Despite public denials from a rep, the British comic plans to cover all the nitty-gritty, sometimes ugly details of their failed 14-month marriage ... Us claims.

"Katy is insulted and feels betrayed that Russell has treated her so poorly," a pal to the "Firework" singer, 27, tells Us. "She will never forgive him. Ever."

For the record, Katy says no one speaks for her.

Although Perry is supposedly "in panic mode" regarding her ex's memoir plans, she's back to work on her ongoing concert tour, commercial shoots and more.

She's taking pains to "limiting interactions" with Brand, another source says of Katy. "He's being so atrocious that she feels like she never knew him."

FYI, he's really not, as far as we can tell.