The parents of Madeleine McCann are to travel to Portugal for the start of a libel action against former police chief Goncalo Amaral, who made claims about them in a book on their daughter's disappearance.

SLIDESHOW: Where Is Madeleine McCann?

The couple plan to attend the opening of the trial in Lisbon on Friday, their spokesman Clarence Mitchell said.

"They only intend to appear at the opening and I would expect that they will return to the U.K. fairly swiftly," he said.

Madeleine was nearly four when she went missing from her family's holiday apartment in Praia da Luz in Portugal on May 3, 2007 while her parents dined with friends nearby.

Despite a massive police investigation and huge publicity worldwide, she has not been found.

Amaral was involved in the initial investigation to find Madeleine but was later taken off the case.

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