James was named director of the video, but hadn't locked down a location for the shoot, so he opted to crash four fans' apartment and film the video there. Caroline, Isabel, Sydney and Hadley were more than happy to accommodate the surprise guests in their Brooklyn pad.
"It's not something you expect to happen when you open the door. We were just discussing our work day, sitting around in our living room. We did not think that was going to happen," Caroline told ET. "... [It was] such an out of body experience to be walking around our house with him."
Sydney said the whole experience was "really fun," adding that "small talk" with the singer and the late-night host was her favorite part. During that small talk, though, Sydney didn't say everything she wishes she would've.
"I started a note on my phone [of] things I wish I had said to Harry," she admitted. "I did not say about a 100 things I wish I said."
Hadley could relate to her roommate, telling ET, "He's so nice, so we had normal conversations [with him]. We were just in shock. It was hard to think about all of the things we wanted to say to him."
That's perhaps why Hadley's favorite part of the shoot was when she and her friends got to dance with Harry. "When we were jumping up and down, that's a once in a lifetime opportunity," she said.
Amongst the four girls there's no argument about who's the biggest Harry fan, as Hadley claims that title with pride. She also has a mega stash of Harry merchandise, which the singer himself discovered while in the apartment.
"There is a lot more where that came from," Hadley quipped of all the merch she has. "... He saw it and he said it was OK. He felt comfortable being around me, so that meant a lot to me. After 10 years of waiting to meet him, he was OK with my level of fandom. I'm sure he's seen crazier. It meant the world."
For Hadley, the whole thing was her "dream come true."
"All I wanted my whole life was just to meet him, just for one second, just to take a selfie, just meet him walk away," she said. "This was beyond my wildest dreams and truly a dream come true. [It was] not even a dream, because you wouldn’t dream something so amazing."
Caroline was likewise thrilled with the experience, telling ET that it's still a blur.
"When we were all sitting around after everyone left we couldn't even remember what happened. It just felt like a haze," she said. "... We can’t ask for anything more in our lives. Our lives are set."
The girls' good fortune didn't end when Harry and James left. Isabel told ET that they not only received "gorgeous flowers" from James after the shoot, but were also treated to tickets to Harry's concert.
"We were just bursting at the seams and screaming the entire time," she said of their concert experience. "... We [have] truly been on cloud nine since."