Story highlights Zimbabwe's President Robert Mugabe accidentally delivered the wrong speech on Tuesday

Mugabe's critics jumped on the incident as a sign the 91-year-old Mugabe is too old for his office and should step down

His spokesman says there was a "mix-up" in the secretarial office

Harare, Zimbabwe (CNN) Zimbabweans generally don't laugh or get excited about President Robert Mugabe's speeches, given the level of poverty and reported human rights abuses in the southern African country.

But an unprecedented slip-up in a speech by the 91-year-old leader on Tuesday has changed the mix.

Instead of a speech officially opening Parliament, Mugabe read his State of the Nation Address, which he had already delivered on August 25.

After the incident, his spokesman George Charamba issued a statement saying: "There has been a mix-up of speeches resulting in a situation where His Excellency the President delivered the wrong speech.

"The mix-up happened in his secretarial office therefore the delivery in Parliament should be set aside. The error is sincerely regretted and corrective measures are being considered."

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