The Duchess of Sussex's father has accused her of cheapening the royals as she and her husband prepare to step back from their duties.
Thomas Markle's relationship with Meghan has been fraught for several years and he missed her wedding to Prince Harry due to ill health.
They are believed to have not spoken since.
Now, in an interview with Channel 5 he has added his thoughts on Meghan and Harry to the mix.
"When they got married they took on an obligation, and the obligation is to be part of the royals and to represent the royals," Mr Markle said, saying it would be "foolish" for them not to.
"This is one of the greatest long-living institutions ever. They are destroying it, they are cheapening it, making it shabby - they shouldn't be doing this."
He also called them "lost souls" and saying they are turning the Royal Family "into a Walmart with a crown on".
Mr Markle, 75, filmed the documentary in his home in Mexico and it's expected to be aired imminently.
He and Meghan were close when she was growing up and he is believed to have paid for her university tuition.
But their relationship is fractured now, and Mr Markle could even testify against his daughter in a legal battle, as she is suing the Mail On Sunday for printing correspondence between them.
His comments in the documentary come as Meghan's half-sister Samantha also spoke about the couple's plan to forge a new path.
Ms Markle said: "From my perception, I feel she did enjoy it when there was the fab four and the photographs of her hair blowing in the wind and the smiling and the contrived British accent.
"But when the public start to criticise the behaviour and expenditure, the tune changed and it became a bit more attribution error, avoiding accountability, flipping the script."
Meghan and Harry will still be known as the Duke and Duchess of Sussex but will no longer be able to use their HRH titles and will not receive any money from the public fund.
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Though they will maintain private patronages with charities and organisations close to them, none of their visits there will be on behalf of the Queen.
The changes come into play in the spring, and they are expected to carry out some final royal duties before then.