Benedict XVI did, although the pope has said that a signed resignation letter exists to be used if he is incapacitated.
Pope Francis hospitalized in Rome following chest pains, infection, will remain 'several days'
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Catholic church law requires a papal resignation be “freely and properly manifested” - as was the case when Benedict startled the world when he announced his resignation to a gathering of prelates at the Vatican in February 2013.
Pope wrote resignation note in case of health impediment
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