Harry met the young boy, who suffered from lung disease, a heart defect, spina bifida and brittle bone disease, in September 2014, and on hearing that Carson had passed away on 2 June 2015, was compelled to write to his mother, Kirsty, and send his condolences personally.
Excerpts from the letter, published in the Liverpool Echo, read: 'I was so very sad to hear the tragic news. Carson made such an impression on me at the WellChild awards last year with his warm smile and hugs.
'Carson was a wonderful young boy and I am delighted to have had the chance to meet him.'
His mum said of her surprise on receiving the royal correspondance: 'My heart burst with pride, I cried, it was so bittersweet but just reflects exactly what we thought of Harry when we met him.
'He is so nice, genuine and really took an interest. I couldn't believe he remembered Carson but like we always said, once met never forgotten.'