Meghan Markle's half-sister, Samantha Grant, is reported to have been taken to hospital after being involved in a car crash following an alleged confrontation with paparazzi photographers.
The 53-year-old is said to have hit the vehicle's windscreen, suffering a broken ankle and fracturing her knee near her home in Florida on Wednesday.
Ms Grant's partner, named as Mark by celebrity gossip website TMZ, said their car hit a concrete barrier after attempting to avoid a photographer.
He told the website the incident happened near a toll booth, where he claimed a photographer veered in front of the couple's vehicle, leading him to swerve.
Ms Grant hit the windshield and fell to the floor mat, he said, adding that - as she suffers from MS - she was unable to lift herself up and that her foot was twisted backwards.
It comes as Ms Markle's half-brother, Thomas Markle Jnr, 51, claimed the family's lives "have been changed forever" since Meghan's relationship with Prince Harry became public.
"There hasn't been a day gone by when the phone hasn't rung or we've not been followed," said Mr Markle, who visited Windsor Castle to see where his sibling will marry Prince Harry, said. "It's placed a massive strain on us all."
Mr Markle Jr's claims came on the day his father, also Thomas Markle, was due to undergo heart surgery and it has been reported that he has successfully had three stents fitted following a reported heart attack earlier in the week.
Video: Meghan Markle Speaks Out About Her Father
Thomas Markle 'heartbroken' to miss wedding
His son, Thomas Markle Jr, told the Daily Mirror that his father will be "heartbroken" to miss his daughter's wedding.
He said: "My dad will be heartbroken that he cannot be with Meg in Windsor to walk her down the aisle. He would have moved heaven and earth to be there.
"My sister's going to be one of the best things ever to have happened to the Royal family. She will be the perfect modern princess."
Meghan's father 'badly in need of help... he's completely on his own'
Pictures of Mr Markle appeared in a number of British newspapers, which it later emerged were staged, prompting him to drop out of the wedding, telling TMZ he did not want to "embarrass the Royal family or his daughter".
But on Monday he missed a call from his daughter and she later told him she loved him in a text message and said she was concerned about his health, the website reported.
Ms Markle's father has come under severe scrutiny and his attendance at the wedding has been speculated on widely following allegations that he posed for staged paparazzi photos.
Ms Markle's sister, Samantha, told The Sun she was worried about her father and claimed she had wired money to the 73-year-old.
She said: "He is badly in need of help. I'm dreadfully worried about him. He's completely on his own."
Despite her parents divorcing when she was six, Ms Markle has remained close to her father.
Siblings accuse Kensington Palace of failing to help father handle media spotlight
Mr Markle Jr also said Kensington Palace should have offered his father more guidance about how to handle the intense media spotlight.
He said: "I wrote to Kensington Palace months ago asking for their aid. We've all been so overwhelmed by the attention and have found it difficult living under such scrutiny.
"We needed guidance from the royals but we didn't get it. Our family was thrown into the limelight and there's been enormous pressure on us all. It's taken its toll on us all."
Amid intense media scrutiny, Ms Grant accused Kensington Palace of abandoning Mr Markle.
Ms Grant, along with her brother Thomas Markle Jr, have not been invited to the wedding and no longer has any relationship with her half-sister.
Kensington Palace declined to comment.
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Prince Harry and Meghan Markle are set to say “I do” on Saturday, May 19, at Windsor Castle. Yahoo will cover the event live from London from 10 a.m. to 3 p.m. BST (5 a.m. to 10 a.m. ET). Bookmark this link to follow along LIVE.