Meghan Markle's half sister said her father was being prepped for surgery and may still attend the wedding.
Samantha Markle made the revelation as she hit back at the media for the "negative slamming" of her dad Thomas, during an explosive interview to Australian media on Wednesday morning.
Speaking from her home in Orlando, Florida, Ms Markle confirmed her father's health problems and said she hopes he'd be well enough to attend the royal wedding on Saturday.
"Everything about him being under an incredible amount of stress - is true and he send me a message he was undergoing heart surgery."
It is believed that Mr Markle, 73, will no longer walk his daughter Meghan down the aisle after an apparent heart attack last week but Samantha suggested it may still be possible.
"He sent me a message that he was prepping for surgery about an hour ago, so it's a little more immanent than tomorrow (Thursday).
"He's been under a tremendous amount of stress amidst health challenges and I hope he pulls through this now and can still go to the wedding."
Ms Markle, who has admitted to organising staged paparazzi photos for her father, denied fueling the media coverage, which has caused her family an "unbelievable amount of stress" in the lead up to the royal wedding.
"When it gets that big it's overwhelming, no matter what your character is truly like, you can't defend yourself against something that big, it's spun out of control.
"They're going to create their own stories whether you speak or not.
"I have a right to defend myself, set records straight which is initially what I started doing - it was never money motivated", she said.