Ariana Grande and Niall Horan were first seen together as they partied in London during the One Last Time hitmaker's concert at The O2 Arena on 1 June.

Grande was spotted leaving the One Direction star's house in the wee hours of 4 June, Irish entertainment website RTE reported. The couple reportedly spent five hours inside the Irish singer's Hertfordshire mansion.

Reports suggest that the My Everything singer arrived at the 21-year-old singer's home on Tuesday night and left the mansion at 3am Wednesday morning, sparking their dating rumours.

However, Grande's spokesperson denied their dating rumours by saying "Ariana is friends with Niall," the publicist told MailOnline. "He had a big party that she attended."

Grande and rapper Big Sean split in April this year after eight months of intense dating and it is rumoured that the Nickelodeon star allegedly used Canadian singer Justin Bieber during her concert in order to hurt the American rapper.

According to recent reports, the One Direction heartthrob has split from his Australian girlfriend Melissa Whitelaw due to the difficulty of maintaining a very long distance romance.

"Niall and Melissa did well to keep their romance low-profile during their time together," an inside source told Hollywood Take. "They were really close and had fun whenever they went out together. But realistically they always knew it was going to be tough, keeping a relationship going with such distance between them."