The actress was surprised to learn that the Duke of Sussex and wife Meghan Markle have watched some of her Netflix show.
The British actress -- who portrayed Princess Margaret in the first two seasons of the Netflix drama -- was asked on Jimmy Kimmel Live! her thoughts on the Duke and Duchess of Sussex watching the show.
"It's quite mad to think that they have actually seen it," Kirby told Jimmy Kimmel on Tuesday's show. "That's something that you sort of always semi-imagine, but sort of thought, 'Oh, you're probably too busy to watch it.'"
Meghan and Harry admitted during their sit-down with Oprah Winfrey that they have seen "some" of The Crown. Kimmel jokingly said that he couldn't imagine someone not watching the full series.
"They probably binged four seasons in one go," Kirby quipped, before adding, "What a crazy life concept to have a show made about literally your grandparents and their lives…And then I guess you know that yours is possibly upcoming."
This wasn't the first time Harry admitted to watching The Crown. He first admitted it during his appearance on The Late Late Show With James Corden, adding, "They don't pretend to be news, it's fictional. But it's loosely based on the truth. Of course it's not strictly accurate, but loosely."
"It gives you a rough idea about what the lifestyle, what the pressures of putting duty and service above family and everything else, what can come from that," he added before being asked by Corden who he would like to play him on the show, with Harry saying Damian Lewis.
ET also spoke with Josh O'Connor, who plays Harry's dad, Prince Charles, on the last two seasons of The Crown, about the prince watching the show.
"Oh, I love Damian Lewis, he's great!" said the 30-year-old actor. "I think the great thing about The Crown is we put together great casts."
"I'm so excited for the next season and everyone who's involved in that, and I'm sure that if it comes to Damian Lewis, it'll probably be a pretty good bit of casting," he added.
See more in the video below.