The star hosted and performed on the hit U.S. sketch comedy show on Saturday, November 16, and, as he opened the latest instalment, the "Lights Up" hitmaker reflected on his successful career.
Harry went on to name "Niall, Liam, Louis..." before trailing off as he pretended to recall the fifth member's name.
"And um, Ringo, yeah that's it," Harry joked. "Just so grateful Simon Cowell grew us in those test tubes".
While One Direction called it quits in 2016, Zayn departed a year earlier, and bandmate Liam Payne recently told Britain's "The Jonathan Ross Show" he can't see the star ever returning to the fold for a future reunion.
"When he left, it wasn't on great terms so I don't feel like it's a thing," the "Stack It Up" star said. "If he didn't want to be here, he shouldn't be here. Which is fine."
After confessing the two haven't been in contact, the star added: "We did a whole stadium tour without him so I feel like it's fine."