In a 2018 interview with Daily Mail, Fergie admitted: "Although we are not a couple, we really believe in each other.
"The Yorks are a united family. We've shown it. You saw it at [Eugenie and Jack's] wedding. My duty is to him. I am so proud of him. I stand by him and always will. The way we are is our fairytale."
Fergie and Andrew sat side by side at Eugenie's royal wedding to Jack Brooksbank in October last year, and even co-hosted the evening reception at the Royal Lodge.
Since then, the more than friendly exes have been at the centre of intensifying remarriage rumours.
"Andrew is doing everything he can to bring Fergie back into the royal fold," a palace source was quoted as saying in the wake of Eugenie's wedding.
"She was at the preview of Trooping the Colour and Lady Gabriella Windsor’s wedding in London, but he’s just not allowed to bring her to official events until they are officially married again."
The Duke of York no longer needs Queen Elizabeth II's permission to remarry Fergie, since the birth of Prince William and Kate Middleton's third child Prince Louis last April pushed Andrew back to seventh in line to the throne.
Fergie was even spotted with Her Majesty the Queen in the Royal Box at Royal Ascot last June.
The monarch has always had a soft spot for her outspoken former daughter-in-law and respects the friendship Andrew and Sarah have maintained over the years, Vanity Fair reports.