Some of the last words Prince Charles exchanged with his late father, Prince Philip, have been revealed.

In an upcoming documentary by BBC One about the legacy left by Queen Elizabeth's husband of 73 years, Prince Charles reportedly reveals he spoke on the phone with the Prince of Edinburgh one day before his death.

The DailyMail reports that Charles and Philip were discussing how to celebrate the big milestone in what is believed to be their final conversation.

"We're talking about your birthday," Charles said to his father in a phone call on April 8, according to the outlet. .

Prince Philip, Duke of Edinburgh during a visit to Hereford, UK, May 1996.

BBC announced earlier this month that the upcoming documentary "Prince Philip: The Royal Family Remembers" will feature all four of Prince Philip and the queen's children: Charles, 72, Princess Anne, 71, Prince Andrew, 61, and Prince Edward, 57. .

With special access to the Queen’s private cine-film collection, this film is an unrivalled portrait of a man with a unique place in royal history - by those who knew him best," the BBC said in a statement.

Mourners including, front row from left, Kate Duchess of Cambridge, Prince William, Prince Edward, Viscount Severn, Lady Louise Mountbatten-Windsor, Sophie Countess of Wessex, Camilla Duchess of Cornwall and Prince Charles during the funeral of Prince Philip, at St George's Chapel in Windsor Castle, Windsor, England, Saturday April 17, 2021.

He was a much loved and appreciated figure and apart from anything else I can imagine he would be so deeply touched by the number of other people here and elsewhere around the world and the Commonwealth who also I think, share our loss and our sorrow," Charles said, speaking from his southwestern England home of Highgrove.

"It is with deep sorrow that Her Majesty The Queen has announced the death of her beloved husband, His Royal Highness The Prince Philip, Duke of Edinburgh.

His Royal Highness passed away peacefully this morning at Windsor Castle," the statement said.