Prince Charles will walk Meghan Markle down the aisle on Saturday when she marries Prince Harry, Kensington Palace has said.
Ms Markle’s father, Thomas, is unable to attend the wedding, after undergoing heart surgery.
The Prince of Wales was “pleased to be able to welcome Ms Markle to the Royal Family in this way”, the palace added.
Prince Harry’s grandfather, the Duke of Edinburgh, will also attend the wedding, Buckingham Palace confirmed.
Prince Philip, 96, has been recovering from a hip operation.
Ms Markle’s mother, Doria Ragland, will take her daughter to the wedding at St George’s Chapel in Windsor.
Ms Ragland will meet the Queen for the first time at Windsor Castle later, accompanied by Meghan, 36, and Prince Harry, 33.
She has already been introduced to Prince Charles and Prince William.
The ceremony begins at 12:00 BST and will be broadcast to the world.
Mr Markle had been due to arrive in the UK earlier this week, but became caught up in controversy over the apparent staging of photographs with the paparazzi.
Speaking to the BBC from Windsor, American celebrity news site TMZ’s Sean Mandell said he had spoken to Mr Markle on Wednesday and that he said he was “doing well” and “recovering from surgery”.
The reporter who broke the story said it became clear for Mr Markle that he would not be travelling to Windsor on Tuesday.
“Chest pains were really being exacerbated by the emotional strain he was under,” he said. “When doctors told him he needed to have surgery, he decided he needed to heed that advice, despite the fact he wanted to be here in Windsor for Meghan.”
“He definitely feels he’s been mis-characterised,” Mr Mandell added. “That’s why he felt the need to speak out when I reached him.”
Ms Markle released a statement on Thursday saying she hoped her father could be given space to focus on his health.
Ms Markle’s mother met William and Catherine and their eldest children, Prince George and Princess Charlotte, at Windsor Castle on Thursday afternoon.
She took tea with Prince Charles and Camilla at Clarence House in London on Wednesday.
Ms Markle will have 10 bridesmaids and pageboys, who are all under the age of eight.
She decided against having a maid of honour, saying she wanted to avoid choosing between her closest friends.
The view from Windsor
By Hanna Yusuf, BBC News
Kelly Hood, Jackie Hood and Maureen Hayward are on their way to Windsor from London Waterloo.
What they’re most looking forward is catching a glimpse of the family: “That’s what we’re there for really, to catch the family as they come down the long walk”, said Jackie.
There was a chorus of “aaaawww” when I told them Prince Charles will be walking Meghan down the aisle.
“She should be a feminist and do it herself, that’s what I was hoping, that she would walk herself down the aisle,” said Kelly.
“But that is actually really nice. In fact, it shows how progressive and forward-thinking the royal family is,” she added.
“It’s such good fun,” said Maureen.
Ms Markle will spend her last night before the wedding with her mother at the luxury Cliveden House Hotel, in Buckinghamshire, about nine miles north of Windsor Castle.
Prince Harry will be staying 15 miles away at the Dorchester Collection’s Coworth Park in Ascot, with his brother, the Duke of Cambridge.
In Windsor, royal fans have been arriving throughout the week, with the rehearsal of the carriage procession on Thursday drawing hundreds of children, parents and pets keen to embrace the party mood.
About 250 members of the armed forces are expected to take part on Saturday and up to 100,000 people are expected to line the procession route.
Thames Valley Police has said it expects the town to be full to capacity by 09:00 BST.