There's a reason whyKendall Jenner and Harry Styles' joint appearance on The Late Late Show went so swimmingly. 

The singer filled in for James Corden as a guest host on Tuesday's episode, during which he and the Keeping Up With the Kardashians star played Spill Your Guts or Fill Your Guts. During the segment, Kendall agreed to rank her siblings according to their parenting skills, while Harry opted to consume cod sperm rather than answer her question of which songs on his last album are about her.

Kendall, 24, and Harry, 25, go way back and have occasionally sparked dating rumors on and off since 2013. Over the New Year's holiday in 2016, the two got cozy on a luxury yacht while vacationing together in St. Barts. The two were also joined by Ellen DeGeneres and wife Portia De Rossi.

"Why are they a good match? Well, they're both super hot, super great, sweet people," Kendall's sister Khloe Kardashian later told E! News. "And if I'm on a yacht in St. Barts if I'm—how old is she, 20? He's 20?—hey, I ain't mad at you, Kenny. Do your thing, girl!"

See photos from Kendall and Harry's Caribbean vacation:

Weeks later, Kendall and Harry attended a private party at the Troubadour rock club in West Hollywood with her mother Kris Jenner. The two appeared to cool things off for a few months. In April 2016, a source told E! News that they were "hanging out again," but were not "officially dating."

In January 2018, Kendall attended Harry's concert in Los Angeles with friends and was spotted dancing and giving him a standing ovation.

This past May, the two rumored exes were all smiles as they reunited at the 2019 Met Gala.

Watch Keeping Up With the Kardashians on Sundays at 9/8c only on E!