Mel Gibson's wife Robyn has filed for divorce after 28 years of marriage.

In the papers -- signed Apr. 9 -- she cites "irreconcilable differences."

"Throughout our marriage and separation we have always strived to maintain the privacy and integrity of our family and will continue to do so," a rep for Gibson, 53, tells Usmagazine.com in a statement.

TMZ.com alleges that "there is no prenuptial agreement" based on source reporting. In 2006, Gibson's fortune was estimated at $900 million. Under California law, community property -- which includes earnings -- is divided 50/50.

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Robyn -- who split from Gibson nearly three years ago around the time of his infamous DUI arrest, according to -- lists the date of separation as "to be determined," which TMZ points out is important because "earnings generally cease to be community property when the couple separates."

(Gibson filed a response to his wife's petition, stating the date as August 26, 2006, TMZ reports.)

Robyn, who has seven children with Gibson, has requested spousal support and attorneys' fees.

She is also seeking joint physical and legal custody of their son, Tom, who turns 10 Tuesday. (Tom is their only child who is a minor.)s.

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Robyn has snapped up attorney Laura Wasser, who most recently represented Britney Spears in her split from Kevin Federline.

The couple has dogged split rumors for some time.

Gibson was recently photographed with a woman who did not appear to be his wife in Costa Rica on March 4.

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Asked at the time if he and Robyn had split, his rep had no comment.

"Mel is on family vacation with his entire family and their friends," a source told Us. "His sons are there with their girlfriends, his pregnant daughter is there - the whole family is there."