According to the 57-year-old, who is Thomas Markle's eldest daughter, Meghan's comments to Oprah about "growing up as an only child" are outright lies.
Taking the royal to court for defamation, Samantha has alleged that the "false and malicious lies" about Meghan's "rags-to-royalty" story subjected her to "humiliation, shame and hatred on a worldwide scale".
But the Duchess of Sussex's legal team have hit back at the allegations, saying that Meghan's comments were a statement of opinion, not fact.
In paperwork filed by the royal's lawyers, they refute Samantha's assertions that she can "disprove that Meghan 'grew up as an only child'".
"But this perception is inherently unfalsifiable. It is hard to imagine a more personal and subjective feeling than how one views their own childhood," the documents read.
"Moreover, Plaintiff's [Samantha's] opposition completely ignores the context of the statement, where Ms Winfrey asked Meghan about her 'relationship' with Plaintiff (to whom Ms Winfrey referred as her 'half-sister on her father's side').
"Meghan's response to that question that she 'grew up as an only child' was obviously not meant to be a statement of objective fact that she had no genetic siblings or half-siblings."
Instead, Meghan's lawyers called the comment a "textbook example of a subjective statement about how a person feels about her childhood."
WATCH: Meghan Markle makes her first TV appearance since Oprah interview
They also slammed Samantha's attempts to sue Meghan over the royal biography Finding Freedom, which documents her and Prince Harry's 2020 royal exit.
Lawyers argue that the Duchess cannot be sued for a book she didn't write.
"Meghan did not make the statements; she cannot be liable for them," they said. "It is that simple."
The Duke and Duchess of Sussex have always denied these claims.
This is far from the first time Samantha has spoken out against her sister or accused her of "lying" about her family and childhood.
Despite regular attacks in the press, Meghan has rarely responded to her half-sister's claims.
This article first appeared on our sister site, Now To Love.
