At the time of the wedding, Harrison's dad, Billy Grier, told The Sun: “Harrison had never been to a wedding before so this was all new to him.”
“But it was a beautiful ceremony and he enjoyed every minute. He was quite excited to do it. Ever since he met Eileidh, they have been inseparable."
His mother, Stefanie Grier agreed: "The two of them just have this magical bond. Harrison has always said that he loves her and that he wanted to marry her."
"Harrison doesn’t really like to play dress up or anything like that but Eileidh has this way of convincing him."
"She has been telling all the nurses that she has a boyfriend and that they are going to get married."
Close friends and family gathered in a meeting room at the Aberdeen Exhibition and Conference Centre, as the children held hands and exchanged necklaces.
A lone piper got the event under way and was followed to a makeshift altar by a procession of costumed superheroes and princesses.
Eileidh was walked into the room by her older brother Callum, to ‘When You Wish Upon a Star’ from Disney film Pinocchio. Her sister Cerys, then read a poem which ended with the words “even if we are apart, I will always be with you”.
The pair then exchanged St Christopher’s necklaces to signify the journey that they had been on together.
And after they were officially declared “best friends forever”, Eileidh and Harrison exited the auditorium where they celebrated with fairy-floss.
However, sadly, Eileidh's heartbroken mother confirmed on Sunday that her daughter had lost her battle with cancer.
Writing on Eileidh's fundraising page (which smashed its £10,000 target), Gail wrote: "With a very heavy heart, I'm heartbroken to tell you all that Eileidh gained her Angel wings at 11.45am on Saturday 1st July.
"Unfortunately it was discovered on Thursday, after an ultrasound scan, that Eileidh's liver was enlarged & full of neuroblastoma."
"This was the most aggressive she has ever had as it grew extremely rapidly. She took her last breath surrounded by her family & cuddled up with blankie."
"She won the hearts of everyone who met her and will be sorely missed."