Jen & John kaput? Plus, Britney's comeback revs up with OK! sit-down, Madonna speaks out on adoption rumors, young Hollywood love-triangle rumblings and the latest smooch news ...

Don't hold your breath waiting for an invitation to Jennifer Aniston and John Mayer's tabloid-trumpeted "wedding of the year." Just a week after OK! detailed their alleged aisle-walk plans (complete with champagne, caviar, a Vera Wang gown and one of her two pooches possibly serving as ring bearer), the actress, 39, and the crooner, 30, have apparently decided to pull the plug on their four-month romance.

"They had a great time together but they are just in different places in their lives right now," an insider explains to People.

Jen goes solo in Los Angeles on Aug. 5.

Pipes in a "mutual pal" to Us, "It is really a cooling-off, not this big, dramatic breakup. These are mature people who talk about things maturely. It's just slowed down."

But the New York Daily News thinks Mayer might be the one throwing himself a pity party, claiming his makeup artist recently had to slather some cream around his eyes because they looked "puffy." (Wait, he has a makeup artist?)

The paper also advances speculation that Aniston has already moved on to someone new, who, depending on whether you believe the National Enquirer, may be a model type, not unlike onetime fling Paul Sculfor.

Still, a pal of the verbose singer-songwriter, perhaps remembering his reunion-prone relationship with Jessica Simpson, doesn't consider a reconciliation outside the realm of possibility.

"He never ends things with a clean slate," the buddy tells People. "He likes to dwell on these relationships and sort everything out before saying goodbye for good."

Meanwhile, a confidant alleges to Us that Jen was clear with John about her "desire for a baby," a supposed spawning imperative featured on the cover of last week's Star.

But another source argues that it's unfair to accuse the former Mrs. Brad Pitt of scaring off the ridiculously tattoo-sleeved troubadour.

"If she said she wants kids and he's not ready, that's not being needy," contends the mole. "It's being honest."

Also citing the kid factor is the London Daily Mirror, which claims Aniston and Mayer originally planned to take a breather before calling the whole thing off earlier this week.

"There's been a bit of tension for some time," a Mayer snitch tells the paper. "They initially opted for a break, hoping a trial split might make them stronger. Sadly, it doesn't seem to have worked. John took the decision to end things as he felt he just wasn't ready for the level of commitment that Jennifer deserved."

The source adds that despite the wedding and baby fever whispers, "Jen didn't want to have kids or marry this year, but she did want to set a timetable for their future together."

Continues the blabby insider, "Initially, Jennifer was furious when he told her of his decision but now she's simply sad -- not to mention a little heartbroken. They have spoken on the phone since the split and are trying to remain on good terms."

But unlike People's source, this one isn't so sure they'll find their way back to each other: "Unless John has a dramatic change of heart, it's unlikely they'll rekindle their romance."

The former squeezes have been flying solo in recent days, with Mayer photographed hot-tubbing with pals in Cabo San Lucas, Mexico, and Aniston putting in appearances at a Los Angeles charity event and a memorial service for Hollywood player Bernie Brillstein.

Jen and John get handsy in Miami last April.

That's quite a change from Jen and John's instantly serious start, which kicked off with a touchy-feely Miami interlude in April.

In the weeks that followed, Aniston tagged along on several of Mayer's concert stops, turning up backstage everywhere from Amsterdam to Milwaukee, and the two enjoyed plenty of hang-time with friends as well as a getaway to Mexico.

They were last spotted together in Los Angeles at the end of July, when they ducked paparazzi as they hit hot spot Villa.

Mayer, for his part, has made no secret of his need to stay interested in the chase.

"If I wake up in the morning and I don't want to get you a coffee, or if I don't see you for a week and I don't want to go figure out something to FedEx you, then we've got a problem," he told Cosmopolitan earlier this year. "You can fake the words I miss you, but you can't fake getting someone a book."

John also discussed his breakup methods during a June interview with the London Telegraph, maintaining that he's always been up front when he's ready to bail out of a relationship.

"And then, when I realized that I didn't wanna wrong anybody by continuing, said, 'I'd rather be a great friend to you than a bad boyfriend,'" he said of his extrication technique. "I swear to God, I have a really good track record!"