Prince Harry met Holly Smallman back in 2015 after her sister, Ruby, had won a WellChild award. The young girl had struggled with health conditions including cerebral palsy, epilepsy, and lung disease.

Sadly, Holly passed away in her sleep last month at the age of 18. The Daily Mail reported that the girl's mother, Hayley Smallman, received a surprise letter via email from the Duke of Sussex.

Prince Harry met Holly Smallman in 2015

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Prince Harry reached out with a touching letter after learning of the news about Holly. The Duke of Sussex is a patron of WellChild and a regular visitor to the annual WellChild Awards.

"I wanted to write and say how saddened I was to hear of the tragic loss of your daughter Holly," the letter began. "I feel so fortunate to have met Holly when her sister Ruby received a Well Child award.

"Holly was evidently a very special and happy girl, despite her significant challenges, and she clearly had an extra special relationship with her siblings. It was a great privilege to spend time with you all, particularly Holly, and I still remember the amazingly creative handmade penguin that Ruby gave me."

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Harry & Meghan send their condolences to the Smallmans

The letter continued: "I imagine words cannot really hope to provide much comfort to you and your family at this most difficult of times. But I wanted you to know that you, and your daughter Ruby and son Josh, are all in my thoughts and prayers."

"Meghan and I send our deepest and most heartfelt condolences," Harry signed off.

The Daily Mail reported that Holly's mother, Hayley, said the Prince's letter meant a lot to the grieving family.

"For Prince Harry to find the time to send this email, to know that Holly made that impact on him and that he cares so much, even in all this private turmoil he's going through, just meant the world to us," she said.