Rotate a camera with a mouse

I have a camera (UCameraComponent on an AActor) that I would like to rotate. I want to rotate the camera about the camera’s right and up axes - to change pitch and yaw. The camera is facing down. I use AddRelativeRotation. There are two ways I go about it. I set a quaternion with Up or Right being the axis, then I get FRotator based on this quaternion and pass it to the function. Or I set FRotator from FRotationMatrix::MakeFromX(Target).Rotator() where Target is a forward looking vector and then I Add() Pitch or Yaw to the FRotator and pass it to the function. Both ways I can get Pitch change functioning more or less as expected, but adding to Yaw and Roll both produce sort of Roll like motion. I checked on the axes - Up, Target and Right are all correct. Thanks.