Singer Madonna arrives at the amfAR Cinema Against AIDS 2008 gala taking place during the 61st Annual Cannes Film Festival near Cannes, France on May 22, 2008. The event raises funds for AIDS research. (UPI Photo/David Silpa)

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Madonna married the British filmmaker in 2000. The couple, who is raising three children together, is not believed to have a prenuptial agreement.

The Times of London said Fiona Shackleton, the divorce lawyer who ensured McCartney retained the bulk of his estimated $1.6 billion fortune, has been counseling Madonna, who is said to be worth about $600 million.

Shackleton also acted on behalf of Charles, the Prince of Wales, in his divorce.

Ritchie reportedly has consulted with the lesser-known law firm, Forsters.

The Times said Madonna's publicist declined to comment for its story.