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For a few minutes on Nov. 7—the day his marriage went from chaotic to kaput—the guy in a Toronto store wasn't K-Fed, he was K-Dad. "He was looking at baby clothing and holding up these little baby outfits," says a photo agency rep who was with aspiring rapper Kevin Federline, in Toronto to promote his debut album while his wife, Britney Spears, was in New York City. "I showed him pictures of my kids and he went, 'Yeah, man, this is the worst thing because I'm gonna be on the road for like three weeks, and I wish [Britney and the kids] would come and surprise me.'"

Just hours later came a different surprise: news that Spears had filed for divorce. Only eight weeks after the pop princess, 24, and her husband, 28, celebrated the birth of their second son, Jayden James (their first boy, Sean Preston, turned 1 on Sept. 14), Spears cited "irreconcilable differences" in dissolving a union that has always seemed a little shaky (one Web site started a divorce countdown the day after their September 2004 wedding). In fact, in the last few hectic days, it appeared to rip at the seams.

"It's about time," says someone close to Spears. "During the whole pregnancy they had problems. She tried to support him as much as she could, but at the end of the day she realized it wasn't best for her and her children [to stay]. She's standing up for herself and making positive changes in her life."

Rumors of a Brit split were rampant: The couple hadn't been photographed together in weeks, and Spears skipped several recent events to promote Federline's album Playing with Fire. Still, the timing took many by surprise. "As far as I knew they were perfectly fine," says Michael Prescott, a family friend from Kentwood, La., Britney's hometown. "I talked to Miss Lynne [Britney's mother] just the other day and she said Britney and Kevin were going to take a vacation trip together to Hawaii, just get away from everything for a few days." The announcement "came as a total surprise," says a Federline pal. "We're all in shock. [We're hoping] it might just be that she's feeling a lot of postpartum emotions and this is something that will blow over."

Yet sources who spent time with Federline in New York City the weekend before Spears filed for divorce say it was obvious something was seriously wrong. Both Spears and Federline were in Manhattan Nov. 3 and 4, ostensibly for a concert and party for his album, "but they didn't spend any time together," says one source. "Britney stayed at the Regency Hotel, he stayed at the Doubletree. And she didn't come to his record release party at [the nightclub] Stereo." By the time a solo Federline arrived in Toronto Nov. 6 "he looked pretty depressed," says the photo agency rep who was with him. "You could see it in his eyes, it was like tears were welling up. It was a really odd feeling talking to him. He was a sad guy."

Spears, on the other hand, had never looked happier. On Nov. 6 she dropped in on David Letterman, her first surprise visit to the Late Show since popping in on May 9 to announce she was pregnant with Jayden. This time she showed up wearing a short black dress and blonde bob wig just to say hi and model her surprisingly svelte post-pregnancy figure. "She looked terrific," says an audience member who didn't recognize her at first. "I thought maybe it was an imposter."

Turns out Letterman just missed another juicy scoop. Spears went straight from the Ed Sullivan Theater in midtown Manhattan to the nearby Sony Studios, where she faxed her signature to the Los Angeles lawyers handling her divorce. The next day, Nov. 7, the lawyers filed divorce papers at the L.A. county superior court.

The next day a chirpy Spears—still in her platinum wig, plus a snug, low-cut dress and black fishnet stockings—had dinner at the Manhattan restaurant Baldoria with four friends. "She was busting out of her dress," one bartender remarked. "Maybe she's out to celebrate tonight." Sure enough, Spears capped off her merry evening by ducking into a Gap—where she bought $300 worth of winter duds, including a striped cowlneck sweater and a white pom-pom hat—and ice-skating at the Rockefeller Center rink. She smiled as tourists snapped pictures and giggled as she nearly lost her balance before sneaking out a back exit.

A few hours later, Federline made his first public appearance since the papers were filed at Chicago's House of Blues Hotel, where he was quickly spirited from his tour bus through the hotel's back entrance. Says a source at the hotel: "He looked depressed—I actually felt bad for him. He looked down the whole time and didn't make eye contact."

Different cities, demeanors and goals—that pretty much sums up their turbulent two years together. Spears, whose spur-of-the-moment first marriage to boyhood chum Jason Alexander in 2004 lasted all of 55 hours, made no secret of wanting to be a mother and live a less public life. "I'm a country girl at heart," she told PEOPLE in February. "I long to be at home. I like that simplicity for my child. I really, really do." But her unlikely marriage to Federline, a former backup dancer from Fresno, Calif., with designs of his own pop stardom, seemed made somewhere other than heaven. "We're an opposites attract," Federline told PEOPLE on Nov. 3, just days before the divorce announcement. "If she gets mad and she yells at me, it just turns me on more, ya know?"

But a source close to Federline says the marriage took a turn for the worse when he headed off on a Las Vegas trip with his friends in late September to party at Tao for the nightclub's one-year anniversary, leaving Britney, who had just given birth three weeks earlier, home alone. "This was her last straw," says the source. "He said, 'I have to go to Vegas.' He didn't have to go to Vegas. He uses any excuse to party. She said, 'I've had enough.'" Not long after that, according to the source, Federline moved out, and has been staying with friends who have a place in the San Fernando Valley.

But the beginning of the end may have been even sooner. "Their relationship changed after the first baby was born," says a source. "Things became more strained. It was overwhelming at times, especially when Britney got pregnant again." Federline, adds the friend, "still loves Britney and their sons so much and has tried to be a good husband and father. He's not pursuing his career as a rapper for purely selfish reasons; he genuinely wants to take care of his family, and this is one way he sees he can do that." Federline himself told PEOPLE on Nov. 6 that "having two kids and trying to do all the business and everything, it's not easy. It's tough but we will make it through this. We're a superpower."

Whatever they were, they endured an awfully awkward final few weeks. At a Halloween/album-release party at the L.A. club Xenii, the couple "got into a massive argument," says a source. According to someone else who was there, Federline's ex Shar Jackson (with whom he has two kids) was also in attendance. As the party wore on, Spears became annoyed with Federline and eventually "went running [out] without her shoes, she was carrying them in her hands," says a source. "She was crying."

After that, they rarely showed up anywhere together. Spears blew off the chance to lend a little heat to his new album by steering clear of a release party at the New York City hot spot Stereo on Nov. 3. The next day Federline dined at the newly opened New York City eatery Corio, but Spears was a no-show. Three days later she filed for divorce.

Now, barring a reconciliation, it's all in the hands of lawyers. The couple signed a prenuptial agreement, but any divorce settlement will have to resolve the custody arrangement for their two young children—something that could be made more complicated by Spears's desire to retain sole decision-making power. (New York City divorce lawyer Nancy Chemtob predicts that Spears will face "an uphill battle.") However they resolve the custody issue, it seems that Spears, for one, is more than ready to get on with her new life. "She was on top of the world before she met him," says a source close to her. "And now she really wants to get her career back on track. I think people are rooting for her. People want her to be happy. But I don't think the public ever liked her with Kevin."

1. DIVORCE

2. HAVE DINNER

3. GO SKATING

Only hours after filing for divorce, Spears and four pals breezed into Manhattan restaurant Baldoria (above), trailed by a paparazzi horde. "No one has ever made a splash like that," said the bartender. Then it was on to the Rockefeller Center rink for a seemingly carefree spin on the ice (left).

For the latest breaking news and photos of Britney and Kevin, go to PEOPLE.COM/BRITNEY

  • Contributors:
  • Michael Fleeman/Los Angeles,
  • Marisa Laudadio/Los Angeles,
  • Lesley Messer/Toronto,
  • Natasha Stoynoff/New York City,
  • Ryan Pienciak/New York City,
  • KC Baker/New York City,
  • Mark Dagostino/New York City,
  • Jeffrey Slonim/New York City,
  • Natasha Burton/New York City,
  • .