The effect of environmental conditions on the fracture behaviour of two types of adhesively bonded joints (wet-aged and non-aged) is experimentally studied under mode II loading. End Loaded Split tests were performed at various temperatures (−55 °C, room temperature (RT) and 80 °C) on non-aged and aged specimens. The non-aged specimens were stored in a laboratory under controlled conditions at RT (23 °C/55 RH) while the wet-aged specimens were exposed to accelerated ageing in an environmental chamber at 70 °C/85% RH for four years. The data reduction was applied using an inverse method and two other direct methods. A good agreement between these methods is observed. The analysis of the obtained results shows that extremely long aging times considerably affect the fracture response of bonded joints under mode II (the fracture toughness of the wet-aged specimens degraded by more than 30%). Furthermore, testing at high or cryogenic temperatures has a significant effect on the fracture response. Indeed, testing at high temperatures was observed to increase the fracture toughness (this increase ranged from 8% to 80%) while cryogenic temperatures increased the brittleness of the adhesive which caused a substantial reduction (more than 25%) in the fracture toughness of the bonded joint.