High-speed rolling element bearings for aircraft engines are custom-made components and operate under high temperature conditions owing to the elevated rotational speeds and loads. Therefore, assessing the various heat generation sources and mechanisms is worth investigating to accurately quantify the overall power loss within the bearing. In this context, a numerical parametric study was performed to determine and locate various power losses inside an aero-engine cylindrical roller bearing. Then, a thermal network model based on Ohm’s law was developed to estimate the operating temperatures of the bearing elements. A series of experiments was carried out on a high-speed rolling element bearing test rig to validate the numerical predictions, such as bearing component temperatures and overall power loss at specific operating conditions. The numerical predictions based on a hybrid approach showed good agreement with the experimental data.