(Reuters) - A French court has ordered Christine Lagarde, the head of the International Monetary Fund (IMF), to face trial over her role in a payout of some 400 million euros ($434 million) to businessman Bernard Tapie, her lawyer said on Thursday.

The case, which has roots dating back more than 20 years, will be heard by magistrates at the Cour de Justice de la Republique, which judges ministers for crimes in office, France’s prosecutor general said.

Lagarde, who is accused of alleged negligence over the Tapie affair while serving as France’s finance minister, said she would appeal against the decision, adding that she shared the prosecutors’ view there was no basis for any charge against her.

“Ms. Lagarde would like to reaffirm that she acted in the best interest of the French state and in full compliance with the law,” said a statement issued by her office.

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Thursday’s court decision came as a surprise as France’s top prosecutor had recommended in September that investigations against Lagarde in the case be dropped.

“A decision like this is incomprehensible,” her lawyer Yves Repiquet told Reuters.

“I sent her a text, she was really surprised and very disappointed,” he said, adding that his client was currently in Washington.

While Lagarde was finance minister, Tapie won French government compensation after selling his stake in sports company Adidas to Credit Lyonnais in 1993. He claimed the now defunct bank had defrauded him after it later resold his stake for a much higher sum.

International Monetary Fund (IMF) Managing Director Christine Lagarde sits for an interview at IMF headquarters in Washington July 1, 2015. REUTERS/Jonathan Ernst

The IMF’s executive board reaffirmed its confidence in Lagarde’s ability to effectively carry out her duties, IMF Communications Director Gerry Rice said in a statement.

France’s current finance minister, Michel Sapin, concurred, saying in New York she was innocent until proven guilty and should not be prevented from carrying out her IMF duties.

Earlier this month, a French court dismissed Tapie’s demand for a further payout of over a billion euros, ordering him instead to pay back the original compensation.