Prince Harry’s ex-girlfriend, Cressida Bonas, paid a  heartfelt tribute to her “darling sister” Pandora Cooper-Key at a memorial service in London on Friday, it has emerged.

Pandora Cooper-Key, a ceramicist, died on July 22 aged 51 after a 24-year cancer battle. She suffered from Li-Fraumeni syndrome – a rare disorder which increases the risk of developing several types of cancer.

On Friday, Ms Bonas, an actress and model, was joined by her late half-sister’s friends including Queen Camilla’s son, Tom Parker Bowles, and her nephew Sir Ben Elliot at St Luke’s church in Chelsea, the Mail reports.

Other guests at the service included Pandora’s half-sister Isabella Calthorpe and her sister-in-law Holly Branson as well as actress Gabriella Wilde.

During her tribute, Cressida said of Pandora: “My heart is forever tied to yours.”

The outlet claimed that Ms Bonas’s moving “letter to Pandora” was written after her death.

The 35-year-old was in a relationship with the Duke of Sussex for two years between 2012 and 2014.

The women’s mother, Lady Mary-Gaye Curzon, said: “Nobody on Earth who ever met Pandora could help falling in love with her.”

The mother of two had suffered from several types of cancer for over two decades. At the age of 26, she was diagnosed with Paget’s disease, a rare cancer of the milk duct, and had a double mastectomy.

She was diagnosed with cancer sarcoma of the sinus at the age of 34, just weeks after giving birth to her eldest son, according to the Times.

By the time of her death, she had also suffered from other cancers.

A death notice in The Times at the time read: “Beloved daughter of the late Edmond Cooper-Key, and Lady Mary Gaye Curzon, adored mother of Bow and Nestor, so much-loved sister of her two brothers and eight sisters and devoted aunt to her nieces and nephews.”

Prince Harry spoke about his relationship with Ms Bonas in his memoir, Spare.

In the book, Harry wrote about their “painfully awkward” first kiss, saying: “I leaned in to give her a kiss, but my aim was off. I could take out a cactus from three miles away from a Hellfire missile but I couldn’t quite find her lips.

“She turned, I tried again on the return trip, and we managed something like a graze. Painfully awkward.”