A nine-year-old cancer patient has struck up a friendship with Kate Middleton, the Duchess of Cambridge.

Leukaemia sufferer Fabian Bate met the Duchess in October when she and Prince William opened the £18 million children’s cancer unit at the Royal Marsden Hospital.

Fabian had been undergoing eight hours of chemotherapy a day when the royals arrived and the family had just found out that Fabian’s sisters Cassia, 11, and Oleander, 17 were perfect matches for a bone marrow transplant.

Fabian told Kate all about his blog, Faith for Fabian, and Kate promised to post on his guestbook.

However, Kate went one step further and wrote him a letter. It is believed Fabian is the first person she wrote to since marrying into royalty.

In the letter Kate said: “Despite the enormously demanding course of treatment you are undergoing, I was so touched by your strength of character, and delighted to hear the news that one of your big sisters will be able to donate bone marrow to you later this year.”

She also said she will keep the Bate family in her thoughts and prayers, something which really touched Fabian’s mother who put out a plea for prayers and said the more prayers going up the better.

Fabian’s mother Lydia Bate, 50, said the princess came straight across the ward and shook her hand.

She said: “She was so friendly and lovely; she asked a lot of detail and said how sorry she was.

“William was absolutely lovely with Fabian; he kept telling him he was such a good boy.

“It just meant a lot to everyone and reinforced for me that they really do a lot for people, the fact that two people can come in and light a room up.”

Fabian is due to have a bone marrow transplant later on in December and his eldest sister Oleander will be the donor.