Recently, renewable energy sources (RESs) are strongly being integrated into power systems due to environmental, and economic benefits due to the deregulation of the energy market. The stochastic behavior of the load and the intermittent nature of RES creates frequency variation in interconnected hybrid power systems. This paper proposed the use of a novel multistage controller, proportional derivative filter type with a 0.85 proportional integral controller PDF+(0.85 + PI) for Load frequency control (LFC). The controller has two sections, the first section deals with a filter-connected PD controller, while the second stage deals with a 0.85 + PI controller employed to maintain the speed of response by overcoming steady-state error and establishing system stability. The PDF+(0.85 + PI) controller gains are optimized using the Grasshopper optimization algorithm. Three different scenarios were investigated. In the first scenario, all system nonlinearities including the Governor DeadBand (GDB) and Generation rate constraint (GRC) were disabled to compare the performance of the suggested controller to other heuristic-based controllers. In the second scenario, the system nonlinearities are activated and the performance with other technique are compared. Finally, the system RESs were included to test the robustness of the controller. The first and second scenarios are compared with the Salp swarm algorithm-based-PID (SSA-PID) controller and the Genetic algorithm-based-PID (GA-PID) controller whilst in the third scenario the dynamic response fluctuation is within the allowable bounds of 0.2Hz. The proposed controller provides superior dynamic system response with the significant performance of an average value of 72.35%, 36.07%, and 49.68% at scenario 1 and 28.16%, 20.31%, and 38.9% at scenario 2 in terms of settling time in change in frequency deviation at area 1, 2, and power tie-line.