Kate Middleton writes letter to 9-year-old cancer patient

A few weeks back, Kate Middleton and husband, Prince William, opened a children's cancer unit at London's Marsden Hospital, and it seems one of the kids in particular, touched Kate's heart.

The Duchess wrote a personal letter to 9-year-old Fabian Bate, who was first diagnosed with leukaemia in 2006 and relapsed earlier this year.

Set on the St. James Palace letterhead, the note (dated October 13) is a heartfelt expression of well wishes to the boy, who is battling leukaemia.

"I was so touched by your strength of character. I will keep my fingers crossed that your health goes from strength to strength," she writes.

In the letter, Kate also promises to keep Fabian in her "thoughts and prayers" and says she admires the boy's "belief and positive energy."

The boy's father, Darrell Date, told PEOPLE that Kate's letter provided a much needed lift for his whole family.

"…it was a massive boost to know that we have someone at Kate's level sharing our journey," he said, adding: "The thought that someone in her position would take that personal interest is a real hope-builder."

"If [Kate] is going to take the trouble to follow our little family situation with everything else going on in the world, it makes Fabian feel special. It gives him a bit more fight to be honest."

Kate's letter to little Fabian