The Irish Sun is reporting that Nialler's aunt died suddenly in her hometown in Mullingar, Co Westmeath.
She will be put to rest tomorrow, meaning that Niall may not be able to attend the services, as he is in the middle of his Flicker Sessions tour.
Susan was married to Niall's uncle Paddy, who is Niall's father's brother.
Her funeral notice reads, "Susan Horan (nee McCann) - O'Growney Drive, Mullingar, Co. Westmeath - September 23, 2017 (suddenly) at her home. Beloved wife of Paddy and dear mother of Haley (Reilly); she will be very sadly missed by her loving husband and daughter, her adored grandchildren Cillian, Eoin and Ciara, son-in-law Stephen, sister Sandra, brother Terry, brothers-in-law, nieces, nephews, relatives, neighbours and friends."
Niall has yet to make any comments on the matter, however his latest Instagram post was him announcing his Mexican tour to be cancelled due to the massive earthquake the country just experienced.
The funeral notice also reveals that Niall's aunty passed away on Saturday, meaning he would have been in Las Vegas performing at the iHeartRadio Festival.
Let us all show some respect and privacy for Niall and his family following this tragic news.