Meghan Markle's father is under an "unbelievable amount of stress" ahead of the royal wedding, her half-sister Samantha has said.
Doubts remain over whether Thomas Markle will will walk his daughter down the aisle when she marries Prince Harry on Saturday.
Mr Markle allegedly staged paparazzi photographs of himself in the run-up to the wedding at Windsor Castle, and it has been reported that he has now withdrawn from the ceremony as a result.
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Kensington Palace declined to confirm whether or not Mr Markle had pulled out but appealed for understanding, saying: "This is a deeply personal moment for Ms Markle in the days before her wedding.
"She and Prince Harry ask again for understanding and respect to be extended to Mr Markle in this difficult situation."
Ms Markle's half-sister, Samantha Markle, said she hoped her father would be at the ceremony.
She told Good Morning Britain that he had health issues, and had been experiencing chest pains and suffered a heart attack.
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"I think he wants to go to the hospital and get checked out," she said.
"I don't know as of today what his plans are, but there's a very real concern. I wanted to see him go (to the wedding), I didn't want him deprived of that.
"But clearly the priority should be whether or not it's safe for him to do that."
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1:11She added that Mr Markle had been pressurised into a "dangerous situation" because of media intrusion.
"He had spoken with press and was doing just that, but when he called me, panicking on the freeway because he's in a dangerous situation being followed by seven or eight cars – I think there have been examples in history of how dangerous that can be."
Earlier, she tweeted to say it had been her idea for Mr Markle to pose for what she described as "positive photos" to try to combat his "bad" portrayal in the press, but said it was not done for money.
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It is thought that if Mr Markle does not attend the wedding, Ms Markle's mother will accompany her down the aisle.
:: Sky News will broadcast live in Windsor the week before the royal wedding with all the build-up to the big day, with exclusive live coverage of the wedding in UHD in a special programme from 9am to 3pm on Sky News and Sky One on Saturday 19 May.
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