It’s midnight and Mariah Carey is sitting with her feet up on the sofa. There’s a bottle of very nice red wine on the coffee table.

She pours us each a glass. We’re in a suite at Las Vegas’s Caesars Palace where she will be performing her chart-topping hits in a reported £40 million two-year deal. With more than 200 million record sales she’s the bestselling singer/songwriter on the planet.

Her distinctive, five-octave voice and gutsy defiance put bums on seats and money in the slot machines. ‘Cheers,’ she says and clinks her glass against mine before relaxing back into the cushions. She smiles. ‘There, that’s better, I’m a little tired. You must be too.’

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Despite her phenomenal success Mariah Carey says that her journey to the top has been no easy ride

Hours earlier I watched as she arrived here to astonishing scenes as thousands of fans brought the Las Vegas Strip to a standstill. Flanked by bodyguards, she stepped Lady Godiva-like from a classic pink convertible in a pair of towering stilettos and a sheer nude gown with a few strategically placed beads.

‘Mariah, Mariah’, the fans shouted as Mariah-the-superstar stood in those impossible heels on The Colosseum stage at Caesars Palace to launch her latest single Infinity.

She wiggles her toes in the way people do when they’re relaxed. Earlier, when she was surrounded by bodyguards to protect her from a sea of clawing people, she looked downright ill-at-ease at times. If not scared out of her wits.

‘Of course there are moments that are uncomfortable when you’re in a beaded dress walking around and you’ve got to put a smile on your face,’ she says.

Last year her six-year marriage to America’s Got Talent host Nick Cannon ended

‘But there’s always a genuine moment when I’m dealing with fans who could be doing anything else but are screaming my name and calling out for me and making me feel warm, accepted and happy.

‘Stardom is a magical yet freakish situation at times. It’s a cliché but very true that at times you feel so alone even when you’re surrounded by so many people. Trust is not very easy for me at all. I want to be a trusting person but I’ve been bruised so many times – not to sound woe-is-me about my life.

'I’m thankful for my fans who make up for the lack of closeness I feel to most people who start out as friends and ultimately take advantage of me. I’m a very loyal person and it takes a lot for me to actually un-friend someone.’ She pauses. Reflects. ‘I’m actually very loyal, to my detriment. Yeah, the past few years have had their ups and downs.’

Mariah has, to put it mildly, been through the emotional wringer recently. Last year her six-year marriage to America’s Got Talent host Nick Cannon ended amid explosive headlines.

It’s been a difficult time, which Mariah has steadfastly refused to speak about. Nick is, after all, the father of her four-year-old twins Moroccan and Monroe. She’s never shed a tear in front of them. She says she daren’t.

‘I don’t want them to see a mother who’s saying, “I’m going through this. I’m going through that.” They’re babies – innocents. They don’t have to see that yet – if ever. So I try to keep everything together because, in some instances, if you cry you’re not going to stop crying.’

Now, Mariah-the-superstar does have something of a reputation as one of the trickiest divas going, but this Mariah sitting beside me is behaving so very nicely, you can’t help but wonder if they’ve cloned her somewhere between the stage and here.

‘Do you have children?’ she asks. (One.) ‘We’re blessed, aren’t we? It’s just doing the normal things with them that’s so special, isn’t it? They’re the greatest experience of my life. They’re my best friends. They’re everything.’ She pauses, and those huge brown eyes cloud for a moment. She’d sooner hand back her five Grammy awards than cause her twins further pain.

Instead, she and Nick put their differences aside to share Thanksgiving, Christmas and Easter as a family. ‘Christmas was a rough time for me personally but I got through it and you know what? It was for the kids. That was the whole thing. I have a song called Side Effects which goes, “I kept my tears inside because I knew if I started I’d keep crying for the rest of my life with you. I finally built up the strength to walk away, don’t regret it but I still live with the side effects.”’

Of course there are moments that are uncomfortable and you’ve got to put a smile on your face

She half-sings, half-speaks these words. ‘That became something I sang over and over to myself because I’ve been through a lot over the last couple of years. I don’t talk about that [she means Nick] because it’s inappropriate but...’

She looks down at her glass and her eyes mist over with the tears she won’t let fall. ‘I’m just getting used to when the kids have days out and overnight stays. I have to get used to that but I’m finding it hard. It is what it is. I want them to have great relationships with all their family and I wouldn’t want to do anything to undermine that.’

Which is all well and good except for... well, now she’s relaxed, we might as well talk frankly: her new single Infinity, it isn’t exactly conciliatory is it? Take the lyrics, ‘You lost the best you ever had… There’s an end to infinity.’

Or, ‘Ain’t no compliments/Ain’t no being friends/Ain’t no false pretence/Ain’t no make amends/Ain’t no come agains/That’s the story, ain’t no happy ends.’ Well, you get the gist. It’s not hard to hazard a guess as to who she had in mind when she wrote the song. ‘Here’s the thing,’ she says. ‘I like to leave it open.’ This time the smile is not forced, just downright mischievous.

Her concern for her children aside, Mariah quite simply can’t talk about her separation from Nick while the divorce is being hammered out. She can, though, write what she pleases in her songs. Her Infinity lyrics were completed two months ago, but she kept them a secret until the single was released at her Las Vegas extravaganza earlier today, attended by the cream of international showbiz reporters.

Needless to say, ‘Mariah disses Nick in break-up anthem’ headlines flashed around the world. The song will be on her new album #1 To Infinity – a chronological compilation of her 18 chart-topping singles – which she will perform for the first time in one production during her Las Vegas residency.

Mariah says she feels blessed to have her twins Monroe and Moroccan

‘Until yesterday some of my best friends hadn’t heard the song,’ she says. ‘I just felt I wanted to keep this one for me until it was time to release it.’ Like they say, revenge is a dish best served cold, although there’s nothing remotely chilly about this Mariah.

‘I wanted to laugh it off,’ she says. ‘But not everybody gets my jokes or humour. Ten years ago if I said three words that didn’t sound well rehearsed it was, “Oh my God, what is she thinking?” I couldn’t care less now.’ She laughs. ‘I don’t care.’

She and Nick married in a secret ceremony at her home in the Bahamas (there are also homes in New York, Los Angeles, now Las Vegas and... I lose count) following a whirlwind six-week romance. He’s 11 years her junior but she truly believed – following an earlier desperately unhappy five-year marriage to former Sony chief Tommy Mottola, who launched her career – that she’d finally found her soulmate.

Within a few short months she was delighted to discover she was going to be a mother, then devastated when an ultrasound scan revealed she had miscarried the day they were due to travel to Aspen in Colorado to celebrate Christmas with friends. ‘I was going to tell them I was pregnant and make little baby ornaments with them because obviously I didn’t know [what had happened] until the scan. That was a difficult Christmas. It was huge. There are really no words and it’s difficult to talk about.

‘That was the lowest point for me,’ she says in a whisper. ‘I wasn’t sure why it happened. I was working on Touch My Body [a song from her 11th Album E=MC²] so I was very thin and working out a lot. I didn’t know you had to stop exercising and stop doing yoga when you’re pregnant. Nobody told me these things.

Mariah celebrating her official arrival at Caesars Palace in Las Vegas, at the launch of her single Infinity

'That’s why it was so scary when I became pregnant with the twins a couple of years later. I was in the house in Los Angeles in that private moment when you take the test in the loo. It was an incredible feeling but, yes, scary. Having the babies was a great high point but being pregnant was not easy.’

Mariah suffered with pre-eclampsia (a pregnancy disorder involving high blood pressure) and gestational diabetes, which causes women without diabetes to develop high blood-glucose levels during pregnancy. Doctors suggested inducing labour at 32 weeks but she couldn’t bear the thought of having her babies taken from her and placed in neonatal care, so she rested in bed for three weeks to give them the best chance she could. ‘I wore a bellyband with an iPod attached to it so the babies could feel the music. I managed to hang on for 35 weeks because I just didn’t want to see them go through things they didn’t have to go through.’

I didn’t feel I fitted in. I didn’t feel like a pretty girl. I didn’t feel like the average person.

Monroe, named after Mariah’s childhood idol Marilyn Monroe, was born first on 30 April 2011 weighing 5lb 3oz and her brother Moroccan followed at 5lb 6oz.

‘I remember sitting there with a nurse and I was so over being pregnant. All I could do was take a bath. I’d thought, “I’m going to work through it. I’m going to do the water birth. I’m going to do this and that.” No way. I couldn’t. I was in so much pain. Please,’ she reaches for my arm. ‘I don’t want to come across as complaining. I couldn’t be more grateful for them or more humbly thankful for them to happen in my life. I’ve never really felt that closeness in terms of family members.

‘These guys are... we’re one and the same. They’re babies but they’re mine and they’ll always, forever be my responsibility. Not all people think that way but I feel I have to fight the dysfunction in my family to get to that place where they know Mummy always comes back – “Don’t worry, it’s always going to be us.”’

Mariah’s childhood wasn’t easy. Her mother was white and her father part-black, part-Hispanic. They divorced when she was three. She missed her father dreadfully, never quite believing he loved her, and she lived with her mother, a tempestuous Irish opera singer.

They moved 13 times to homes that were always poorer and more Bohemian than anyone else’s. The family stuck out like a sore thumb in their predominantly white neighbourhood on Long Island, New York. People burnt crosses onto their lawn and the family dog was poisoned.

Mariah started singing at four and used to hide under the kitchen table scribbling her own songs when everything became too much.

‘I didn’t feel I fitted in. I didn’t feel like a pretty girl. I didn’t feel like the average person. I felt below average. I had my friends who had darker skin, different textured hair and others who were fair. I was in a neighbourhood where you had to be one thing or the other. It was awkward for me, and because my parents were divorced there was no one to say, “This is who you are and this is how to deal with it.”

Mariah performing on stage in Las Vegas

‘But I always knew I had music. That was my saving grace. I think the greatest gift to me is that I can express myself in songs. It helps me get through some of the hardest times of my life. It also helps me celebrate some of the best times.’

Among those hard times was an accident on the set of a music video 18 months ago that left her with a dislocated shoulder. She was due to perform with the New York Philharmonic Orchestra in a fundraiser for the victims of Hurricane Sandy the next night. Against the advice of doctors, she went ahead.

‘I didn’t not want to do it so I performed in a sling with bruises all over me in this sparkly dress. I was in tears. It was moving, but the tears weren’t out of self-pity. I was in pain and singing a very sad song. The doctors said the injury was the equivalent of being hit by a truck. They were looking at me in shock because they couldn’t find a pulse in this arm.

‘I was bedridden for a while, but I didn’t really want to talk about it because I was worried I wouldn’t regain the use of the arm. Being stuck in bed was terrible but I had really good physical therapists who came and moved the arm up and down for me to retrain my mind in that muscle memory. I got through it but it wasn’t easy.’

She shakes her head and sips her wine. ‘I’m still recovering from it now in terms of getting my body back to where it was. Before that I was in a really good place and I think, “Why?” She slaps the extra inches of flesh she’s trying to shift in the way we women do. Then she shrugs.

‘There’s a reason for everything and that’s how I look at it. Last year was not a pleasant year for me, but I’ve had unpleasant times before and it hasn’t stopped me.’

Being a mum has helped Mariah overcome everything she’s faced recently. There’s constant conflict between her need to sing, her need to create and the dreadful wrench of being apart from her children.

‘It’s tough because you want to make it up to them for when you’re not there but you don’t want to spoil them. I work at home whenever I can but even that’s being away from them because it’s a big house. And I have to be selfish sometimes with my voice and say, “I have to go to bed now.”’

Their latest thing is Paddington Bear, she says. ‘Have you seen the movie? Isn’t it great? I loved it and I didn’t think I would but it was something my dad read to me when I was little. We love Paddington. Don’t you hate having to be the one to say, “You have to go to bed now?” But I try to give them as many boundaries as possible – everything from, “Please” and “Thank you” to “Not too long on the computer” because it sucks the life out of us. I’d rather they’re interacting and have a personality...

‘Sometimes I sing with my daughter. We sing in conversation, “I love Mummy,” and I’ll sing back to her. We have a whole conversation in song. When you’re doing that it’s really writing a song. It’s freestyling.

'That’s the new version of me as a little kid hiding and writing music, but I still do that. I still sit up and write and work on music and love it. I use it as escapism. I love all forms of creativity. I still love acting. I did Precious [the 2009 film for which she was highly praised in her role as a dowdy social worker] and got lots of offers, but then I got pregnant and so I wasn’t able to explore them, as I didn’t want to tell the world in the beginning because with twins it’s a high-risk pregnancy.’

It’s late now. Again she touches my arm. ‘You know what the theme of Infinity really is? You have to love yourself to survive all the challenges life may put in front of you and just keep going. Then you can love others who are close to you.’

Does she? There has been speculation she’s dating her long-time friend, 46-year-old film and music video director Brett Ratner, who directed Rush Hour and produced the Horrible Bosses movies, after they spent a recent holiday together in the Caribbean.

‘Brett and I are like brother and sister,’ she says. ‘I think we have a similar work ethic and are both eternal kids.’ So you’re not with anyone? ‘No, I’m definitely single.’ Anyone you’d like to be with? She laughs. ‘Drink your wine.’