Sarah Ferguson spends what would have been their 30th anniversary with Prince Andrew

Prince Andrew has always remained good friends with his ex-wife Sarah Ferguson despite their divorce 20 years ago. The duo is committed to co-raising their two daughters, Princesses Beatrice and Eugenie, and still regularly spend time together at family gatherings.

On Saturday the Prince and the Duchess of York spent a day at the races with their younger daughter Eugenie.

But royal watchers noticed that the date – July 23 – had a special significance for the ex-couple. It was 30 years exactly since Andrew and Sarah said "I do" at Westminster Abbey, in front of the Queen and other members of the royal family.

TAP TO VIEW GALLERYSarah Ferguson and Prince Andrew Sarah, Duchess of York and Prince Andrew married 30 years ago last Saturday

A source explained to the Daily Mail: "She and Andrew were going to spend time together in the evening on Saturday to mark their anniversary, and Andrew invited her along to Ascot to enjoy the day. He was representing the Queen, who was in Scotland."

The pair were pictured chatting at the King George VI weekend at Royal Ascot, although Sarah and 26-year-old Eugenie looked to have spent the majority of the day together.

The Princess was chic in a white summer dress and gold strappy sandals, while her mum also opted for a similar monochrome look.

Sarah Ferguson and Princess Eugenie watching horses race The Duchess spent the day at the races with her ex and their younger daughter Princess Eugenie

Prince Andrew's invitation to his ex-wife would explain why Sarah, 56, was allowed into the royal box for the first time in years. Last month she curtseyed to the Queen and Prince Philip at Royal Ascot, although she watched the races from a separate balcony next to the royal box.

Earlier this year it was reported that Sarah had plans to apply for Swiss residency, as she spends many months a year in the exclusive Verbier resort, living in her and Andrew's $22.5 million ski chalet.

Sarah Fersuson and Princess Eugenie at the races "She misses Andrew and her daughters," a source said

However it seems that Sarah has not permanently moved out of the 30-room Royal Lodge in Windsor.

A friend added to the Daily Mail: "The truth is that Sarah is spending more and more time back at the Royal Lodge, where she lived for years, and less time in Switzerland. She misses Andrew and her daughters."

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