In this paper, we design a joint caching and trajectory optimisation (CTO) solution for unmanned aerial vehicles (UAVs) assisted video multicasting (UVM) in 6G networks. To do so, the mobile users (MUs), who have the same interest of videos, are grouped into different clusters. We then formulate a CTO problem and solve it for the optimal number of videos to cache and the optimal set of UAV’s stops to fly throughout, to serve the MUs in different clusters at maximum video delivery capacity. Simultaneously, a next shortest hop problem and the travelling salesman problem are solved for optimal trajectories, and thus reducing the flying energy consumption of the UAV. Simulation results are presented to analyse and demonstrate the benefits of the proposed CTO solution for the UVM in 6G networks.