Ariana Grande Parties The Night Away With One Direction Star Niall Horan

Former Nickelodeon star Ariana Grande is in London to open the U.K. leg of her "Honeymoon" tour. The pint-sized pop princess opened up the tour last night with a sold out show at London's 20,000-capacity O2 Arena. Amongst the packed audience at Ariana's show was One Direction star Niall Horan. According to the Daily Mail, hunky Niall and pretty Ariana could not get enough of each other's company, so they set off to a swanky club in London's famous West End to party the night away.

Ariana and Niall, together with a group of friends, headed off to Cirque Le Soir, a raunchy burlesque club in the heart of London's Soho district. According to the Mirror, Ariana arrived at the London hot spot "showing off perfect pins" and washboard abs in a matching black mini-skirt and crop topped. Grande topped off her look with black high heels and a matching clutch bag.

Niall chatted with Ariana backstage before jumping a cab to join Ariana at the night spot. Ariana and Niall were reported to have been partying until after 3 a.m. before the pair left the club separately. The Daily Mail reports that Ariana's former boyfriend, Nathan Sykes, was also along for the party. Recent reports have speculated that Ariana and Sykes have been drawing close since Grande split with boyfriend Big Sean. If Ariana and Nathan are getting close again, it would seem unlikely that "Niriana" will become a thing anytime soon.

Sadly for Ariana and Niall, the night was cut short as three fire trucks attended the club as a result of an electrical fault. Ariana and Niall left separately through a back entrance.

The Telegraph was less than complimentary about Ariana's first U.K. show, describing it as having "spectacle but no soul." Telegraph reporter Alice Vincent did concede that Ariana is "undeniably talented," but states that the 90-minute show contained only "a handful of solid songs."

Grande opened her set with "Bang Bang," which she performed solo, but Vincent claimed that this was one of the show's few highlights.

She said, "as the evening wore on it became clear that this was one of a handful of solid songs, a small peak in a set that was given a delivery as mechanical as its staging."

Whilst Vincent was clearly not impressed by Ariana's constant costume changes, Niall Horan seemed to enjoy the proceedings much more. Horan even took to Instagram to post a video of Ariana onstage.

Niall claimed that Ariana Grande "has the most incredible voice" he has ever heard.

[Photo by Larry Busacca / Getty Images]