A US judge has dismissed a defamation case brought against the Duchess of Sussex by her half-sister.

Samantha Markle was suing Meghan over comments she made in a Netflix documentary and a 2021 interview with Oprah Winfrey.

In her ruling, Judge Charlene Edwards Honeywell found these comments were either opinions, substantially true, or did not plausibly defame Samantha.

The case was dismissed with prejudice, meaning she will not be able to refile.

Samantha had taken issue with Meghan's comment, made in her interview with Winfrey, that Samantha had changed her surname back to Markle when her half-sister had started dating the Duke of Sussex.

But in her ruling Judge Honeywell said: "The court has taken notice of the fact that [Samantha] used the surname Rasmussen in September 2016 and Markle two months later, soon after [Meghan's] royal relationship was first reported.

"Therefore, the gist of the statement - that [Samantha] switched to her family name a short time after it was reported [Meghan] was involved with Prince Harry - is true."

The lawsuit also took issue with Meghan's remarks on how close they were growing up, with Meghan telling Winfrey: "I grew up as an only child, which everyone who grew up around me knows, and I wished I had siblings."

Judge Honeywell ruled that this was Meghan's expressed opinion of the relationship.

The judge added that Samantha had failed to identify any statements that could support a defamation claim.

According to the court document, this was Samantha's third try at amending her complaint against Meghan, with whom she shares a father, Thomas Markle.

She first took legal action in March 2022, alleging the duchess had defamed her by giving information to an unauthorised biography called Finding Freedom and by discussing their relationship with Winfrey on live television.

The case was thrown out last year after Judge Honeywell found the duchess could not be liable for the contents of the book because she had not published it.