News quickly spread Wednesday that Nick Lachey and Jessica Simpson have split and that their storybook marriage is officially over. But Nick and Jessica claim it isn't so.

Wednesday, Lachey's publicist issued this statement to "Extra" on behalf of both of the "Newlyweds," saying, "Nick and Jessica have not separated. Rumors to the contrary are simply not true."

Sunday, Simpson flew solo (and without her wedding ring) at her sister Ashlee's 21st birthday party at the Las Vegas club Pure, inside Caesar's Palace.

"Nick is not here tonight," Ashlee confirmed Sunday night. "[Jessica] came by herself today to celebrate with me."

Despite the couple's denials, Us Weekly is sticking by their story, saying that Lachey and Simpson have walked out on their marriage. The magazine reports that just two days after Ashlee's party, the couple called it quits.

But according to Us Weekly's Caroline Schaeffer, Lachey and Simpson have not been together for close to two months. "Now we know the reason they are not wearing their rings," Schaeffer said. "I think for a long time people have said this is a marriage of convenience for business reasons. It wasn't the right time to split, so for a long time they have been having separate lives, but staying together in public."

Lachey and Simpson were last seen together on September 11th at a football game. But just days later, Simpson was again solo and again without her wedding ring.

For months now Simpson has repeatedly told "Extra" that there was no truth to the constant breakup rumors. "It's hard because you don't want people to believe that you and the man of your life aren't in love anymore," Simpson had said.

In August, Lachey did the same when subbing for Regis, saying, "Everything is absolutely wonderful in love, marriage and life."

But Us magazine claims their sources say this time, the split is real. "People say it's only a matter of time before they file for divorce," Schaeffer said.