Songfacts®:

• "Sin Fin" is a pop/bachata fusion where Romeo Santos and Justin Timberlake promise an everlasting love to the object of their affection (the title translates as "With No End"). They recorded "Sin Fin" for Formula, Vol. 3, the third installment of Santos' Formula trilogy.
• Santos has form for tailoring a bachata with non-Latin superstars on his Formula records. "Promise" finds him hooking up with Usher, and "Odio" is a collaboration with Drake.
• Collaborating with Justin Timberlake had been on Santos' bucket list for a long time, but the two had never met and had few connections. After a year of gauging his interest, Timberlake came on board and Santos presented him with "Sin Fin." Timberlake dug it and Santos couldn't have been more thrilled with his input.
  
  "What I respect about JT is he not only recorded his vocals, but he turned that song that now I feel was at 30% into something completely different for the better," Santos told Billboard. "He changed the melody, the lyrics; he wrote, he produced. There was a moment where I was at the studio and he was directing my guitarist. To me, that was surreal: JT is producing a bachata."
• Fans of Santos' group Aventura will know the Latin superstar's fandom of Timberlake goes back a long way. On Aventura's 2002 album We Broke the Rules, Santos took 'N SYNC's song "Gone" and translated it into Spanish.
• To help him come up with a song that made sense with his story, Santos recruited longtime collaborator Rico Love. The producer had worked on "Promise"' and "Odio" with him, and he wanted to keep the tradition.
  
  He also linked up with producer Danja (with Timbaland he'd co-produced all of Timberlake's 2006 album, FutureSexLoveSounds). "The reason why I did that is because I wanted it to feel authentic," Santos told Apple Music. "I really wanted it to have his essence. JT threw his spice in there producing, tweaked some melodies, songwriting. He just gave it his magic."
• "Sin Fin" topped Billboard's all-genre Latin Airplay chart, marking Santos' 21st #1 on the tally. You won't be surprised to learn it was Timberlake's first.