"I think his voice is one of those that’s really rare and I think he’s really special and wonderful and it’s really amazing to work together," Swift says in the video, which she shared on Instagram on Friday.
"It's amazing when you get to people that you hang out with," she continues. "The question of ‘Will we get along?' is already answered."
The "Shake It Off" singer also called the 24-year-old British singer, who is dating Swift's pal Gigi Hadid, "incredibly talented."
"I feel really lucky to get to do this song that I’m really proud of with him," she says adding, "Everybody involved has been amazing."