Rihanna breaks down in tears during Irish gig and Conor McGregor makes an appearance backstage

The Umbrella singer took the stage at the Aviva Stadium at 9.15pm for the start of the U.K. and Ireland leg of her Anti tour and appeared visibly upset about something as she performed her opening number, Stay.

She then started crying while singing her second track, Love the Way You Lie.

Rihanna offered no explanation for her late arrival or her tears and proved she's the consummate professional by soldiering on with the show and belting out a total of 24 tunes.

The singer appeared overwhelmed by the support of her Irish fans as she took a moment to take in the sight and sound of thousands of concert-goers chanting her name.

It seems her Irish fans picked her up and she took a moment during the show to tell the crowd, "I only have ever in my life heard an audience of people scream so loud that they sound like one voice and that only happens in Ireland, in Dublin... Thank you so much."

UFC champion Conor McGregor was also spotted at the Aviva gig, alongside longterm girlfriend Dee Devlin. The pair were seated in a corporate box but were seen singing and dancing to the singer's biggest hits.

The Bajan singer brought the couple backstage after the gig and posed for a number of photos with her superfans. She shared a photo of herself with McGregor on her Instagram account, captioning it: "Met @thenotoriousmma #ConorMcGregor backstage last night! So much heart! Thanks for your kind words!"

Although she may be one of the world's most popular performers, Rihanna failed to sell out the gig, despite heavy promotion since Christmas.

Fans outside the venue speculated that her ticket sales dwindled due to the vast amount of gigs on offer this summer.

"We bought our tickets at Christmas because we thought it would sell out straight away but everyone in Ireland is going to other festivals," said Bray fan Jasmin Anderson.

"I am a massive Rihanna fan. This is my second time coming to see her."

Meanwhile, superfan Michelle Garland said she had been getting ready all day to see her idol.

"I am a big Rihanna fan, I was at the last concert, I love her. I have been getting ready since about 9 o'clock this morning and I have been in town since 6pm."

Rihanna has quite a lot going on in her personal and professional life at the moment including ongoing rumours she's dating rapper Drake and the fact she has just bought her dad a house in Barbados.

She has also just returned to the U.K. top five with her new Calvin Harris collaboration This Is What You Came For and launched a new perfume, called Crush.

The bad news is Rihanna is facing legal action from a Nigerian concert promoter amid allegations she scrapped a 2013 performance - and kept her hefty fee.

Megalectrics boss Chris Ubosi claims he arranged the gig for May, 2013 with two people who introduced themselves as representatives for Rihanna, Jay Z, and his Roc Nation firm. The two parties struck a deal for the Diamonds hitmaker to perform a 65-minute set for $425,000 (£292,260), and Ubosi made three early payments, totalling $160,000 (£110,000).

He then received a request from Rihanna's team seeking to postpone the show, which Ubosi agreed to, as long as the pop star publicised the new date on her social media accounts, reports TMZ.com.

The rescheduled concert never materialised, and now Ubosi has filed suit against the two stars and Roc Nation executives in a bid to reclaim his funds after his initial requests went unanswered.