Byline: Richard Simpson Showbusiness News Editor
MEL Gibson's wife of 28 years has filed for divorce, setting the stage for one of the most expensive marriage break-ups in legal history.
Under Californian law, Robyn Gibson could take half of her husband's [pounds sterling]640million fortune.
She lodged papers in Los Angeles Superior Court weeks after Gibson was pictured frolicking on a beach in Costa Rica with an unidentified brunette.
The Australian-born actor is said to have become close to a Russian brunette on the set of his most recent film, but denies he has had an affair with the woman, a musician known simply as Oksana.
The court papers filed by 52-year-old Mrs Gibson cited 'irreconcilable differences' as the reason for the split.
It was reported last night that she and her husband, 53, have been living apart for almost three years.
The couple have seven children, six of whom are grown up. Mrs Gibson is seeking joint custody of the youngest, Tom, who is ten this week.
She and Gibson are not understood to have a prenuptial agreement.
Despite the irreconcilable differences cited by Mrs Gibson, many in Hollywood believe the real reason behind the split is her husband's close relationship with Oksana.
She is one of the artists on the actor's recording label Icon and has been in the U.S. recording an album.
Gibson denies that she is anything more than a colleague, but the pair have been snapped coming out of his trailer on the set of The Edge of Darkness, which is due for release this year..
Gibson, a staunch Roman Catholic, was one of the highest-paid and most popular actors in the world in the 1990s, winning best director and best picture Oscars for his 1995 film Braveheart.
He has adopted a lower public profile since his controversial 2004 hit movie The Passion of the Christ and his 2006 arrest for drink-driving in Malibu, when he launched into an alcohol-fuelled tirade against Jews.
Not long before his arrest he was photographed partying with female admirers.
'The incident definitely took a toll on his …