It's perhaps the most shocking scene of all in the controversial mini-series The Kennedys.
Her parents, Rose and Joe Kennedy, Sr., are horrified to discover Rosemary doesn't recognize them.
It's the dark secret that the Kennedy family tried to keep under wraps for decades, says Laurence Leamer, the author of The Kennedy Women.
"Joe Kennedy, Sr. was a man who thought he could take care of any problem and Rosemary was a problem," says Leamer.
Rosemary was a beautiful 23-year-old woman, the third child in the storied family.
Rosemary's true story can be found in the leather-bound diaries she kept before the tragic lobotomy that changed her forever. The entries are filled with mundane details of Kennedy family life, such as this entry from 1937:
"We all played Touch Foot Ball."
The mini-series depicts Rosemary throwing wild tantrums, but her diaries show a sweeter side.
In May 1937, she wrote: "Went to the Savoy Grill with Jack Kennedy."
Her childlike handwriting reveals she was probably mildly mentally challenged.
"She had the mental age of a 12- or 13-year-old and she was a beautiful young woman and her brother Jack would go to dances and shepherd her because these guys would start hitting on her and she really didn't know quite how to behave with that."
She wrote about a date with a boy: "He gave me violets to pin on my coat. We went to the Plaza […] I had a grand time with him."
Her father worried that Rosemary would become sexually active and he feared she'd get pregnant and disgrace the family, a scene depicted in last night's episode of the miniseries.
So Joe Kennedy, Sr. had Rosemary secretly lobotomized without telling anyone.
"Only 500 of these operations had been done in the entire world and never, never on a young woman who was mildly intellectually disabled. It was unheard of," Leamer tells INSIDE EDITION.
Unlike the scene depicted in the miniseries, Leamer says Joe and Rose Kennedy never visited Rosemary together after the operation.
Leamer continues, "It's absolutely absurd. And that's the kind of liberties that there's no reason or excuse to take."
Instead, she was transferred to a Catholic nursing facility in Wisconsin. The Kennedy family didn't speak about her again until Joe Kennedy, Sr. died in 1969.
That's when Eunice, the mother of Maria Shriver, began overseeing Rosemary's care and even dedicated the Special Olympics to her.