Samantha Markle worries Duchess Meghan and Prince Harry "will never find true happiness".
The Duchess of Sussex's half-sibling has claimed she fears for Meghan's son Archie and she "does worry about his future".
Writing in an opinion piece for The Sun newspaper: "It is clear Meghan cares for Archie, but I do worry about his future. There doesn't seem to have been a lot of consideration given to his cousins George, Charlotte and Louis and how often he will see them. Harry has put Meghan above his brother, father and grandmother. A house divided cannot stand. I am worried that Meghan and Harry will never find true happiness. They could not find contentment with the Royal Family, will they be able to find it away from them? Maybe they will meet up with counsellors who can help them to heal the wounds."
And Samantha - who has not spoken to the Duchess since 2014 - has claimed she has "ripped through the Royal Family like a tornado"
In the lengthy piece, she added: "My sister has ripped through the Royal Family like a tornado. With this historic institution close to collapse, we have to ask whether peace can really be found ... Meghan knew the social requirements of joining the Royal Family. She should have asked herself if she was willing and able to behave in accordance with the expectations.
"Her Majesty's words show great diplomacy but Meghan's behaviour has so far not been diplomatic. A diplomat wouldn't fall out with her own family ... She watched the media taunt and torture my dad, never springing to his defence like a true humanitarian would ... The Queen, at 93, shouldn't have had to face the stress of seeing her family torn apart. Meghan hasn't stepped forward to minimise the damage."