At first it was supposed to be only John, but then John decided to take Paul with him and David Bailey didn’t like it, he just wanted John, but John insisted to have Paul with him. During the photoshoot Bailey said there was a lot of tension between John and Paul, and he also said that he tried to capture the “animosity” between them. He failed though, cause the photoshoot is the most beautiful and romantic thing ever.
Also, John seemed to really like this photoshoot because:
He had this photo in his studio in 1967.
And I assume he kept it until he divorced from Cynthia and left this house to live with Yoko.