Ashleigh Sokie, 20, got her hands on the garments after the 21-year-old singer rented a house in Augusta, Georgia, which is owned by her boss, during the US Masters golf tournament last week and was asked to do his laundry - but then claimed she planned to keep his intimate items.
Ashleigh was told by her boss to wash the items - which included Calvin Klein boxers and a Chelsea soccer team training kit with his initials - and quickly took to her Twitter and Instagram accounts to post pictures of herself posing in the star's clothes as well as garments belonging to his bodyguard Mark Jarvis.
She wrote: "My boss let me wash/wear Niall's clothes because his washer broke last night at his rental house in Augusta.
"I got to fold his underwear and a few of Mark's shirts also. She owns the company that he rented his house through! His washer broke & she was too busy so asked me to wash them.(sic)
She also wrote: "I'm keeping his underwear."
In her first post, which has since been deleted, Ashleigh said alongside a snap of her wearing the garments, as well as a shot of Niall and his bodyguard sporting the same clothes: "washing @niallhoran's clothes because his washing machine broke . . . excuse me while I pass out.(sic)"
According to The Sun newspaper, the pretty brunette has since deleted her Twitter account after receiving a torrent of abuse from fellow One Direction fans.