Mad Max's visit to the movies could cost him $450m

Mel Gibson's surprise red carpet appearance with his new girlfriend ups the ante in his divorce case

The leading man is one of the Hollywood's most bankable stars. His female counterpart is a mysterious Russian with the voice of an angel and an intriguing link to James Bond. The plot involves a spurned wife, a near billion-dollar fortune, and an increasingly messy divorce.

Mel Gibson's suddenly turbulent private life took another step towards summer blockbuster status last week, when he pitched up at the Los Angeles premiere of the new X-Men movie showing off a glamorous new girlfriend: a singer and former employee called Oksana Grigorieva.

The appearance, just a fortnight after the Oscar-winning actor's wife of 30 years, Robyn, unexpectedly filed for divorce, raised the ante in what – with at least $900m (£600m) at stake – promises to be the most expensive Hollywood split in history.

"Mel has been single for almost three years," was how his spokesman explained the pictures showing Gibson, 53, hand-in-hand on the red carpet with the 39-year-old brunette. "It's nice to see him getting out and enjoying himself."

Maybe so. But few things could have been better designed to rile Robyn Gibson, who separated from her husband in 2006 and filed for divorce citing "irreconcilable differences" after the actor was photographed on a Costa Rican beach embracing Ms Grigorieva.

Gibson seldom attends film industry events. Some wondered if Wednesday's appearance marked the start of a "re-branding" in advance of November's release of Edge of Darkness, his first film since a drink-driving arrest in 2006, when he derailed his career by telling a Jewish police officer: "Jews are responsible for all the wars in the world."

Others speculated that Gibson may be softening up his public for a bombshell announcement. The US TV show Access Hollywood has reported that he's actually been with Ms Grigorieva for three years, and the musician is reported to have informed friends that she is pregnant.

The Russian singer has "form" for stepping-out with action heroes who boast Irish ancestry: her 12-year-old son is the product of a long-term relationship with the former James Bond Timothy Dalton. Ms Grigorieva was brought up in Ukraine and emigrated to the UK at the age of 20 to be a care worker, but subsequently studied at the Royal College of Music and launched a career as a pianist and singer.

Further speculation surrounds what Gibson's church will make of the relationship. The actor is a member of a conservative Catholic sect that does not recognise the authority of the Pope and follows an antiquated ideology dating back to the 16th century.

The divorce's greatest impact on his daily life, however, is likely to be financial. Gibson has built up an enormous fortune, making the bulk of his wealth from The Passion of the Christ, which he produced and bankrolled. Costing $30m, the film was released in 2004 and became a commercial sensation, generating $611m at the box office, along with tens of millions of dollars in DVD sales.

Since almost every penny Gibson owns was generated during his marriage to Robyn, which lasted almost three decades, he is likely under Californian law to have to surrender half of the $900m fortune.

A crumb of comfort may come from the fact that this week's outing is unlikely to have damaged his financial prospects. "In California, there is nothing wrong with dating someone when you are separated," said the LA divorce attorney, Lynn Soodik, this week.