The funnyman, who voices meerkat Timon in the film, admits he was nervous about meeting the Duchess, aka Meghan Markle, in London after receiving a list of red carpet protocol from the royal's staff.
"Before you meet them they email you this whole list of very official protocol about what you're supposed to say... and 'don't speak until you're spoken to', but we didn't really know if they wanted us to do that," Eichner tells "Good Morning America". "It feels a little strange and we're American, so I was panicking about what to say...".
"I think I just muttered, like, 'Pleasure to meet you...' I didn't bow; bowing felt weird to me. But they were great."
"The Lion King" star and the Duchess both attended Northwestern University in Illinois, and they quickly found some common ground when she noted they went to the same college.
"We ended up having this very casual conversation about our acting teachers at Northwestern," he adds.