"Stacy hoped they would be together long-term.
"It was a big breakthrough to spend time with his parents. But over the last few weeks George has pulled away from her."
The couple recently spent several weeks at Clooney's villa on Lake Como, Italy, and scooting around Europe.
Keibler seemingly added fuel to the split rumours when she flew solo at Vera Wang's show during New York Fashion Week on Tuesday.
Asked why Clooney wasn't tagging along, she told E! News: "I don't know, ask him."
The Sun also claims that the couple is expected to release a statement announcing that their relationship ended amicably.
The tabloid got the statement part right.
A rep for Clooney has since issued a statement slamming the split report.
"A story published by a London tabloid, The Sun, concerning George Clooney and Stacy Keibler is not true," his rep told Gossip Cop. "[It's a] total fabrication designed to sell newspapers."
As for Clooney's no-show during Fashion Week...
"New York Fashion Week probably isn't high on George's bucket list," the rep quipped to the New York Post, adding "They are still together."
The pair went public with their relationship in September 2011, stepping out together at the Toronto Film Festival.
Clooney was married once - to Mad Men actress Talia Balsam from 1989 to 1993. He's since vowed that he will never trot down the aisle again.
"I was married. I gave it a shot," Clooney told CNN's Piers Morgan last year.
"I've proven how good I was at it, and I just ... I'm allowed one."
The silver fox previously dated Italian model-actress Elisabetta Canalis, but called time on their two-year romance in June 2011.
"We are not together anymore," the pair said in a joint statement at the time.
"It's very difficult and very personal and we hope everyone can respect our privacy."
Their break-up was announced just two weeks after Canalis spoke of her continuing "fairytale" with Clooney, and her desire to be a bride.
"I am a firm believer in marriage, in the future I will be married," she told Italian magazine Chi. "But for the time being I am happy as I am, I don't need anything to confirm how happy I am.
"I am very happy at the moment - thanks to my man and my fairytale is continuing. We are a couple that never gets bored."
FAST GOSSIP
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* Chris Evans says Captain America sequel starts shooting in March.
* "We'll do it eventually" - Kate Hudson on getting hitched to Matt Bellamy.
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* Conspiracy theory video claims Kristen Stewart cheating photos are fake.
* Watch - Robbie Williams makes solo comeback with new Candy video:
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- Rumour Has It
