Derulo, who boasts over 37 million followers on TikTok, has recorded several videos with Smith, including a video in August where Derulo appeared to knock out Smith's front teeth while practicing his golf swing.
On Ellen, Derulo said Smith's team reached out and said the actor was a fan of Derulo's content.
"We started off with one video. That went super crazy, and then we just kind of kept it going," Derulo said.
"It's been incredible because he's always been somebody that I looked up to growing up. So to be doing all these crazy videos that people are loving is pretty awesome," he added.
Derulo said he's seen "all kinds" of wildlife in Smith's yard while filming.
"Pulling into Will's house, I don't know if they were placed there but I saw a deer, I saw little rabbits," he said. "I was like, 'Did they place those there?' Like, come on, this is crazy."
Derulo said he first met BTS at an awards show a couple years ago and reconnected with the group.
"I think it's amazing that two different people from all over the world -- I mean, you have Josh that's from New Zealand, you have myself, American, and you have this massive K-pop group, and you put them all together. I think it's amazing," he said.
Derulo released his fourth studio album, Everything is 4, in 2015. He has released four singles in 2020, "Savage Love (Laxed - Siren Beat)," "Coño" with Puri and Jhorrmountain, "Don't Cry for Me" with Alok and Martin Jensen and "Take You Dancing."