'The arena was huge. I mean, I knew this girl was famous, but this is as big as the stadiums I would play in during my One Direction days, and those were fucking enormous. I look out the window of the tented black vehicle I was in and see the hundreds of thousands of fans waiting outside, all dressed in skirts or dresses for the big event. "I told you Harry, this girl is huge." Frank speaks up from beside me, snapping me out of my stare. "I didn't have to come to one of her fucking shows to…