Meghan Markle and Prince Harry have a "toxic relationship", according to the Duchess' half-sister Samantha Markle.
Samantha is preparing to unite with her father and brother for their "last ever interview" just one week before King Charles' Coronation.
In a world exclusive, the family members will speak to Channel 7's Taylor Auerbach to share unseen family videos and "an extraordinary message".
In a teaser clip for the interview, which will air on Sunday, Samantha shares her thoughts on her half-sister's romantic life.
"They're really unhealthy for each other, it's a toxic relationship," she said as a video showed Meghan and Harry united and holding hands.
Despite Samantha's comments, Meghan and Harry have always appeared united after they started dating in 2016.
The pair enjoyed a fairy-tale wedding two years later and now live in Montecito, California, with their two children Prince Archie and Princess Lilibet.
Broadcaster Taylor Auerbach announced the Markle family interview on Twitter as he shared an explosive trailer.
"WORLD EXCLUSIVE: This Sunday on @7NewsSpotlight - Meghan Markle as you've never seen her before.
"For the first time, the Markles unite with an extraordinary message on the eve King Charles III’s coronation. These hidden tapes will stun the world! Only on @Channel7," he wrote.
The clip starts with a video of Meghan being driven around in a convertible wearing a tiara and prom dress.
A voiceover said: "The world has never seen Meghan like this, the homecoming queen."
The clip then cuts to a shot of journalist Taylor speaking to the Markle family, as he said: "This will be your last interview ever."
The voiceover continued: "Treasured memories, home truths and secret tapes are all coming out."
Speaking to the cameras, Samantha claimed: "She would still be a waitress if it wasn't for dad."
Meghan's brother, Thomas Markle Jr, added: "We're not going to go away. This is going to change everything."
Meghan's father Thomas Markle made a passionate plea to his daughter as he asked: "How can I fix this?"
The interview will premier on Channel 7's Spotlight on Sunday ahead of King Charles' Coronation.
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