After coming back from confronting the Supernatural Elders, Rex stayed inside the castle.
Now that he has dealt with the imminent threat that might jeopardize his plan, he now needs to think of his next moves while the grievous injuries that he suffered from the fight are being healed slowly by the Luna Energy from Evelyn.
It was the same situation as when he got back after fighting with the Executor.
Since Evelyn needs to be around him in order to quicken the healing process, she's sitting on his lap. Both of them stayed still for half an hour before eventually, Rex snapped out of his thoughts and realized something.
Everyone was doing their own thing, and the throne room is empty except for them.
But Rex realized that the silence inside the throne room is very loud, he realized that Evelyn hasn't said a single word to him, and she even faced the other direction, giving him the cold shoulder which is very unlike her.