T. rex was not an apex predator: an apex predator eats other predators, and T. rex ate herbivores.

Palaeontologist and reader in zoology at Queen Mary University of London

I have a problem with the term apex predator because ecologically, apex predators are generally defined as things that eat other predators. So a great white shark is, because it's eating stuff like tuna and sea lions, which are themselves predators, so it's a predator of predators. Whereas people love saying lions are apex predators, and they love saying T-Rex is an apex predator. They're eating herbivores.