As Lauer promised, Middleton discussed her sister's wedding and the subsequent media attention.
"We saw it as a family wedding," the 30-year-old said. "I didn't realize the scale of it until afterwards. We really saw it as a family getting together and doing their bit. To me, it was just performing in front of a lot of people, just not the world. It was surreal!"
Middleton added that she was "embarrassed" by the reaction to her bridesmaid's dress -- and her backside.
"I think the plan was not really for it to be a significant dress," she said. "Really just to sort of blend in with the [wedding dress] train."
Middleton, who's in the United States for a 3,000-mile charity bike race, also told Lauer that she didn't expect the pitfalls that come with fame.
"It's hard sometimes. I have felt publicly bullied a little bit," she said. "It is quite difficult. I'm actually just paving my way just trying to live a life like any 30 year old."
2014: The Year in Fashion [PHOTOS]
Polly Bergen, Emmy Award-winning actress, dies