Leah Hession, six, was given the chance to meet her idol prior to attending the band's gig at Croke Park in Dublin, Ireland in May (14).
The youngster lost her battle with a rare form of kidney cancer this week (ends20Jul14), and Horan has mourned her loss in a series of posts on Twitter.com.
The Irish singer shared a picture of himself hugging Leah along with the message, "RIP Leah , it was an honour to have met you! Very brave young lady! Thoughts are with Leah's family at this time!"