Mel Gibson's wife files for divorce

Mel Gibson's wife Robyn files for divorce after 28 years of marriage

Mel Gibson's wife, Robyn Gibson, has started what could be one of the most expensive break-ups in history – by filing for divorce after 28 years of marriage.

Robyn lodged papers in Los Angeles Superior Court just weeks after Mel was allegedly snapped frolicking on a beach in Costa Rica with a younger Russian woman.

Under Californian law, Robyn - a former nurse - could be entitled to up to half of Mel's £640 million fortune, as she never signed a prenuptial agreement.

The court papers filed by Robyn, 52, cite 'irreconcilable differences' as the reason for the split.

Rumours suggest that Gibson has grown close to the Russian musician, Oksana, on the set of his new movie, although he denies an affair.

Robyn states the date of separation as 'to be determined' in the court papers, but Mel named 26 August 2006 – a month after his controversial arrest for drink driving.

The couple have seven children, six of whom are grown up, and Robyn is seeking joint custody of the youngest, Tom, who is ten this week.

Although 'irreconcilable differences' have been cited, many people believe Oksana is the main reason behind the split.

She is one of the artists on the Australian-born actor's recording label Icon and has been in the US recording an album.

Gibson - who can command up to £17 million a movie - 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.