On the strength of sheer star power alone, a collaboration between Prince and Madonna in 1989 would have been a huge smash single. And yet, they buried "Love Song," their collaboration from her hit album Like a Prayer.

Granted, in the title track, "Express Yourself" "Cherish" and "Keep It Together" -- all of which reached the Top 10 (and the Top 20 "Oh Father") -- she was hardly lacking for radio-friendly material. Maybe it's because the track is hardly a high mark in either of their careers. "Love Song" has a typically solid late-'80s Prince groove that suits Madonna well and a decent chorus, but there's no vocal chemistry between the two.

"We were friends and talked about working together," she told Yahoo Music in 2014, "so I went to Minneapolis to write some stuff with him, but the only thing I really dug was 'Love Song.' We ended up writing it long-distance, because I had to be in L.A. and he couldn't leave Minneapolis, and quite frankly I couldn't stand Minneapolis. When I went there, it was like 20 degrees below zero, and it was really desolate. I was miserable and I couldn't write or work under those circumstances."

It's been suggested that Prince also contributed guitar to several other songs on Like a Prayer, but co-producer Patrick Leonard could only remember that he plays on a portion of the title track.

"When you start 'Like a Prayer,' the guitar that you hear before the door slams," Leonard told Billboard. "That's Prince. ... [Madonna] sent him something to play on and he played on it and sent it back. And we didn't feel that what he did served it. ... There's a heavy guitar in the choruses and when I heard it, I thought, 'Did we use his guitar in those bridges?' Because the sound is similar to the first sound [in the opening], but it's not exactly the same. ... But I know for a fact that we did use that [Prince] thing as the intro, because we just thought it was crazy and really cool. I seem to recall that that's all we used, but I could be wrong."

Hear Madonna and Prince Perform "Love Song"

Prince and Madonna's friendship seems to have had its ups and downs. It's been rumored that they dated for a few months in the mid-'80s, but five years after "Love Song" she had some harsh words for the way that both he and Michael Jackson created a veil of mystery around themselves. "If they would just come outside and mingle with humanity," she told the Los Angeles Times, "everything would benefit - their art, and whatever relationships they may have. ... I had dinner with Prince once, and he was just sipping tea, very daintily. I was stuffing food down my face and I was like, 'Aren't you going to eat?' [She mimics a delicate, whispered "no."] And I thought, 'Oh my God!' I have this theory about people who don't eat. They annoy me. It's something about being in control."

In 1996 Prince released "Dinner With Delores," which could possibly have been about Madonna. In addition to making fun of the titular character's appetite (both for food and sex), he sang about a woman whose "bell's just a-broken since 1984 / Dancing like a white girl on disco dirty floors" and implored her to "introduce the carpet to something other than your knees."

But even though, in the lyrics, he was unable to forgive "Delores," Prince and Madonna apparently made up. After his death, her tour manager Guy Oseary posted a picture of the three of them from 1999 and revealed that, a few years ago, he floated the idea of a Madonna/Prince "Royalty Tour" past the two of them. Madonna was up for it, but Prince's response was, "The world isn't ready for this, it's too big."

Oseary also said that, after Madonna's concert in St. Paul in 2015, which included a shoutout to him, Prince invited everybody back to Paisley Park for a late-night performance. "After the sixth song of the set," reported the Current, "Prince leaned down and whispered something back and forth with Madonna, and then hopped back up to his keyboards and simply said, 'Cool.'”