The actresses, who developed a close bond after starring together in 'The Killer Inside Me' in 2010, have allegedly gone their separate ways since the blonde beauty began dating Muse frontman Matthew Bellamy four years ago.
A source told RadarOnline.com: "Kate has wrecked the friendship and Jessica pins the start of their troubles to the beginning of Kate's relationship with Matt a few years ago."
Kate, who shares two-year-old son Bingham with Matt, has reportedly adopted the mindset that she's "rock and roll royalty" since becoming engaged to the musician in 2011.
The source explained: "Unfortunately, Kate has become not a nice person since she's been with Matt.
"It's sad but Kate and Jessica's friendship is completely done. They used to be so close, too."
Rumours that Kate and Jessica's friendship had deteriorated began to swirl last month when the 'Something Borrowed' star celebrated her birthday.
Kate, 35, was joined by Demi Moore, Reese Witherspoon and Nicole Richie, at the No Name Bar in Hollywood, but Jessica, 33, was no where to be seen.
However, the brunette beauty - who has daughters Honor, five, and Haven, two, with her husband Cash Warren - has been busy with her business The Honest Company, which creates toxin-free household goods, nappies, and body care products.