Being able to do a duet with Beyonce is no easy task. And Ed Sheeran knows it.

“I have an email address I email [to get in touch with Beyonce],” he revealed to Entertainment Tonight, adding that the singer’s email address “actually changes every week.” “So I emailed that and we got on the phone, and it’s been in the works since May… Obviously she had twins [in June], and we finished [the song] in September, so I’ve been holding onto it since then.”

Their duet “Perfect” was released last Thursday.

“The original version of ‘Perfect’ was just an acoustic guitar and she rung me up and was like, ‘I don’t know how you feel about this but I’ve taken all the instruments off it and it’s just gonna be acoustic guitar,’ and I was like, ‘Ah that’s great, because it used to be that!'” he revealed. “Then when we got in together, it wasn’t so much notes, it was very much like a back and forth thing, like, ‘What’d you think of this?’ Or ‘What do you think of this?’ and [we were] probably in the studio for four hours.”