One of the main objectives of walnut crossbreeding programmes is to produce cultivars with late leafing dates. Sixteen years ago, a walnut crossbreeding programme was initiated by Prof. Mehmet Sütyemez, and now a new walnut genotype, namely 'Ahir Nut', has been generated with a leafing date that starts later than all commercially-famous walnut cultivars in the world. The present study describes this walnut genotype. For a detailed analysis, 'Ahir Nut' was compared with two French-origin walnut cultivars, i.e., 'Franquette' and 'Ronde de Montignac', which have had the latest leafing dates until now. In an experimental orchard in Turkey, the leafing date in 'Ahir Nut' was 14 May, whereas the leafing date in 'Franquette' and 'Ronde de Montignac' were 23 April and 25 April, respectively. This approximately 3-week difference between 'Franquette' and 'Ronde de Montignac' to 'Ahir Nut' reveals how valuable this genotype is for walnut breeding studies. The harvest dates for 'Ahir Nut', 'Franquette' and 'Ronde de Montignac' were 4 October, 3 October, and 7 October, respectively. The defoliation date for 'Ahir Nut' was 4 December. The nut weight and kernel percentage of 'Ahir Nut' were calculated as 11.61 g and 49.84%, respectively. Remarkable phenological traits were found in 'Ahir Nut', making it a promising option for future walnut cultivation. In the present study, the late leafing date of 'Ahir Nut' prompted further research into the molecular and walnut crossbreeding potentials. This new genotype has been conserved as an important genetic resource for future walnut breeding programmes around the world.