Lara Spencer listed the six-year-old royal's school classes during a segment on ABC's Good Morning America.
After Spencer said ballet, some members of the studio audience laughed, as did the presenter and her fellow host George Stephanopoulos.
"Oh, he looks so happy about the ballet class," Spencer said, as images of George popped up on the screen.
She then claimed William said his son "absolutely loves ballet".
"I have news for you, Prince William, we'll see how long that lasts," she said. "I mean, he might."
The reaction to Spencer's comment was swift.
Actress Rosie O'Donnell put a video on her Twitter account saying Spencer's comment was "ridiculous".
"It's like bullying on national TV.
"Boys who take ballet are cool," she said.
— Debbie Allen (@msdebbieallen)August 23, 2019
Director and choreographer Debbie Allen, who worked on 80s TV show Fame, said "this is just not cool".
"Look at the great contributors to the world, in society. Men that have studied dance (such as) Steve Jobs. Hello."
Choreographer Brian Friedman, who has worked with stars such as Britney Spears and Beyonce, said the presenter should be "ashamed".
"Growing up as a dancer I was bullied horribly which is exactly what this is," he said.
"She is teaching the word that it is ok to laugh at boys for dancing and that is so sad. Just think about the young boys who may have seen this and could quit their passion at her expense."
Spencer later apologised for her "insensitive comment".
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"My sincere apologies for an insensitive comment I made in pop news yesterday," she said.
"From ballet to anything one wants to explore in life, I say go for it.
"I fully believe we should all be free to pursue our passions.
"Go climb your mountain - and love every minute of it."