Her decision draws a line under one of Hollywood’s most tempestuous and talked-about unions.

Spears, 24, filed her petition at the Los Angeles Superior Court yesterday, citing irreconcilable differences and seeking sole custody of her two sons — Sean Preston, 14 months and Jayden James, eight weeks — with only visitation rights for her husband.

The timing, on the day of the midterm elections, appeared to have been chosen to counter the inevitable blaze of publicity.

However, the petition listed the date of separation as Monday, the day the couple returned from New York.

Also on that day a Los Angeles judge embarrassingly threw out Spears’s lawsuit against the celebrity magazine US Weekly, over allegations that she and Federline had made a sex tape and were worried about its release.

The judge ruled that the allegations were not defamatory because Spears had “put her modern sexuality squarely, and profitably, before the public eye”. The ruling did not address the question of whether the story was true or false.

Although there always had been doubt about the durability of their 25-month marriage, the divorce papers appeared to come out of the blue. Sources close to Spears said that there had not been one thing that had prompted the divorce, but that the relationship had broken down over time. But Spears’s surprise appearance on David Letterman’s chat show, also on Monday may have been intended as a pre cursor to news of the divorce, paving the way for a relaunch of the single sex symbol.

Spears made a quick, apparently unscheduled visit to the New York studio, popping on to the set to greet Letterman. She wore an eye-poppingly short mini-dress that showed off her new svelte figure.

Some of Spears’s fans blamed Federline — “K-Fed” — for the slide in her career. He was derided as a fame-seeker and gold-digger, riding on his more famous wife’s coat tails.

Her career has been in freefall since she got married, with two back-to-back pregnancies and a public mauling over her choice of husband, fashion sense and public behaviour, including driving with Sean Preston on her lap.

The pair met when Federline was working as a dancer on Spears’s tour. He was still in a relationship with Shar Jackson, who was heavily pregnant with their second child at the time. He left Jackson for Spears before the child was born. She warned the pop star that Federline would never settle into married life.

Tensions between the couple have arisen in the past over Federline’s disinclination to work or to play the family man. They separated temporarily last year after Spears reportedly lost patience with his drinking, gambling and visits to strip clubs.

Federline recently relaunched his career as a rap singer and actor, with the financial backing of his wife. He has traded heavily on his association with Spears, and his first single included the lyrics: “Don’t hate me because I’m a superstar, and I’m married to a superstar.”

He and Spears signed a prenuptial agreement on the advice of her lawyers, to protect her fortune.

The marriage was Spears’s second. Her first, to her childhood friend Jason Alexander, was annulled 55 hours after they married at the Little White Wedding Chapel during a trip to Las Vegas.

Family lawyers flew to Las Vegas the following morning to press for the annulment. Mr Alexander later complained that she was pressured into ending the union and that he was coerced into signing the papers.

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