Harry and Meghan’s children currently bear this surname — Archie Harrison Mountbatten-Windsor and Lilibet Diana Mountbatten-Windsor.

If he had actually gone through with the name change, someone like Lilibet would have ended up as Lilibet Diana Spencer.
Such a decision would likely have been deeply upsetting for King Charles, considering he was the one who gave him the Mountbatten surname in the first place.
This comes shortly after Meghan spoke about her personal connection to her name in her Netflix series With Love, Meghan.
“I don’t think anyone in the world knows that Meghan Markle has eaten Jack In The Box and loves it,” her friend Mindy Kaling remarked, following Meghan’s revelation about enjoying the fast food.

The Duchess shared that she found it amusing when Mindy kept referring to her as “Meghan Markle.”
“It’s so funny you keep saying Meghan Markle — I’m Sussex now,” she said. “Once you have kids, you start thinking, ‘No, I share a last name with my children.’”
She added, “I didn’t realize how much it would matter to me, but it really does. It’s like saying, ‘This is OUR family name — our little family name.’”
Mindy responded warmly: “Well, now I know, and I love it.”