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That was fast.

Heidi Montag has fired Aiden Chase, a Malibu-based psychic whom she hired last week to replace husband Spencer Pratt as her manager, has learned.

On Monday, Montag, 23, began shooting a cameo in the comedy Just Go With It, starring Adam Sandler, Jennifer Aniston and Nicole Kidman. When reached for comment, Montag's rep told Us Thursday: "Aiden had nothing to do with securing Heidi's role in the movie."

But a source tells Us that Montag was "horrified" when he showed up on set, "demanding a significant portion of her Hills money."

The source adds that when Chase, 40, recently followed her as she filmed MTV's The Hills, he tried to "move onto Audrina [Patridge]," whom he not only offered his healing/spiritual services but also asked to be her manager, the insider tells Us.

Said the source: "He's this creepy older guy who is clearly preying on these young girls. It's awful."

The source adds that fame is going to Chase's head: He is has now hired his mother as his manager, claiming she once served as Halle Berry's manager, says the source.

"The guy thinks he's famous now -- it's ridiculous," said the source. "He's referring to himself as the most famous psychic in the world."