With fewer than 9000 individuals, Aloidendron pillansii is listed as Critically Endangered, yet the timing and drivers of its decline remain poorly understood. We aimed to rectify this by examining long-term population dynamics at Cornell's Kop using repeat photography, ecological monitoring, simulation modelling, and climate analyses, and compared these with regional patterns of climate and vegetation change. Between 2004 and 2012, juvenile numbers (<1 m tall) were relatively stable (37-45 individuals), with recruitment slightly exceeding mortality. From 2013, juvenile mortality increased sharply, coinciding with the 2017-2019 centennial drought and, to a lesser extent, plant removal, resulting in a 51% decline by 2024. Adult numbers declined more slowly, from 42 plants in 2004 to 31 in 2024. Approximately half of adult losses occurred between 1937 and 2004, likely reflecting senescence of older cohorts. Range-wide size-class patterns indicate aging populations in the north and younger populations in the south, with Cornell's Kop intermediate. Since 1979, regional climate trends show declining rainfall, longer dry seasons, rising temperatures, and decreasing vegetation productivity. Overall, the species exhibits a dual decline: recent drought disproportionately affects juveniles, while adult losses reflect aging cohorts, with population replacement increasingly constrained by climate change and human disturbance.