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It's a story that has ugly celebrity scandal written all over: The famous rocker-husband of an Oscar-winning actress enjoys a public make-out session with a blond starlet.

It's also a story that could result in legal action.

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Chris Martin, aka Gwyneth Paltrow's more musical half, and Kate Bosworth are preparing to take on Star over a report in its latest issue that contends the two were spotted locking lips at a U2 concert in Las Vegas on Oct. 23.

"I couldn't believe my eyes," a spywitness purports to the tab. "There was Chris totally making out with Kate in front of other people. At first I thought it might be Gwyneth, but when she came up for air, it was clear the woman was Kate!"

Continues the seemingly traumatized onlooker, "They weren't even shy about it … they held hands and kissed."

RELATED: See pics of stars showing a little PDA

The PDA accusation has produced swift denials all around.

"This story is completely fabricated," Bosworth's rep insists to Wonderwall. "Lawyers for both Kate and Chris are pursuing their remedies against Star magazine as we speak."

Paltrow's spokesman also dismisses the report, telling us, "The story is another fabrication."

RELATED: Check out pics of Kate Bosworth and other stars at the Scream Awards

(And considering that Gwyneth and Chris, who are parents to Apple, 5, and Moses, 3, have long avoided being photographed together, we have a hard time buying that he's suddenly become so indiscreet.)

So, what touched off the tabloid item?

A source explains to Gossip Cop that Kate, who was most recently linked to easy-on-the-eyes "True Blood" star Alexander Skarsgard, is a "great friend" of both Gwyneth's and Chris' and "has been for years."

But, the mole insists, there is nothing at all "romantic" about Bosworth's association with the Coldplay front man.

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