Did Chris Martin Cheat On Gwyneth Paltrow?

Gwyneth Paltrow in Paris last month.

GOOP's hubby may have done something slimey.

A new story has emerged that Coldplay rocker Chris Martin seems to be playing around behind wife Gwyneth Paltrow's back. Apparently Martin was spotted a few weeks ago getting cozy with another famous blond American woman at a U2 concert.

It's said Chris Martin, 32, and Kate Bosworth, 26, were seen kissing last week at the U2 concert in Las Vegas. Witnesses say that the pair did little to conceal their mutual interest, carrying on right out in the open while the show took place before them.

The pending report comes from a tabloid -- but as one site states, the story cannot be ignored. Apparently Chris Martin may have had a relationship with a "civilian" in 2007, which is said to have been kept quiet.

We hope it's not true and that Gwyneth Paltrow won't be joining Kate Gosselin's club...although the glimpses that we get into the lives of the GOOP guru and the TLC mom are both rather disturbing these days (with the exception of their adorable children)...check out our story on Kate Gosselin's Monday night interview with Natalie Morales here.