Yukiya Amano, the head of the United Nations nuclear watchdog, has died on the day he'd been expected to announce his retirement. The 72-year-old Japanese diplomat became the International Atomic Energy Agency’s director general in 2009 and oversaw an intense period of diplomacy in Iran and North Korea. Amano was planning to leave his position in March next year, well before the end of his term ended in 2021, and was due to announce his retirement Monday. The nature of his illness hasn’t been publicly disclosed—he had an unspecified procedure last September and has looked increasingly frail ever since, according to Reuters. “The Secretariat of the International Atomic Energy Agency regrets to inform with deepest sadness of the passing away of Director General Yukiya Amano,” the IAEA said in a statement.