A word of advice for publicists: If you're going to make up a phony romance for one of your clients, make sure she's in on the plot. Jessica Simpson's alleged love affair with singer John Mayer fell apart Tuesday as Simpson disavowed the relationship on The View. Simpson's after-the-fact denial—paired with Mayer's pooh-poohing of the claim on his blog—caused no small amount of consternation at People and Us Weekly, which splashed the story on their covers last week after receiving all-but-official assurances it was for real.

How did it happen? Insiders, in chorus, answered that question in two words: Rob Shuter. Sources say the publicist, who was pushed out of Dan Klores Communications several months ago after repeatedly getting caught at mischief, was the prime mover behind both the People and US stories. "This was 100 percent Shuter," says one person involved in the situation. "He broke all the rules of the game. He's a pathological liar. I wonder how much Jessica even knew what he was up to."

Others agree with that analysis, though some speculate that Simpson's father, Joe, and an executive at her label, Epic Records, stirred the story as a way to drum up interest in Simpson's new album, which has sold sluggishly since its recent debut. A report in the new issue of Star blames Shuter and unnamed Epic "bigwigs" in the "dating deception." (An Epic spokeswoman called the claim "ludicrous.")

That's not to say there's no kernel of truth to the claims. Sources in both the Mayer and Simpson camps agree the two may be engaged in a casual fling, but nothing that "makes her heart skip," as People's cover put it. A rep for the mag says People stands by its story, while Us Weekly, which treated the item a bit less credulously, is set to publish a follow-up in its new issue.

Shuter denies planting the story, insisting: "We just don't comment on Jessica's relationships." Not on the record, anyway.