Mariah Carey has warned Beyonce that carrying twins is ''hard''.

The 46-year-old singer is thrilled her friend - who already has five-year-old daughter Blue Ivy - is expecting two babies with husband Jay Z, but found during her own experiences carrying her and ex-spouse Nick Cannon's children Moroccan and Monroe, five, that a multiple pregnancy takes its toll.

She said: ''The last time I saw her, I was doing my Christmas [show in New York City,] and she came to my show and brought her daughter. It was really, really sweet.

''I just wish her and Jay all the best.

''It's really hard having twins. I just mean in general, going through the physicality of having twins was really, really difficult for me. I had a tough time.''

However, the 'One Sweet Day' singer insists the discomfort was all worth it.

She added to 'Entertainment Tonight': ''There's nothing like it. They're the best.''

The 'I Don't' singer - who is dating backing dancer Bryan Tanaka - recently caused a stir when she posted pictures of herself working out in high-heeled shoes, but she insists there are benefits to her unusual choice of footwear.

She said: ''This is not the first time I've worked out in heels people. I remember the first time I did this on Cribs and everyone was like, 'Oh my gosh, she's working out in heels! What is she doing?' I'm like, 'I'm being serious!' Then I was just like, 'Let me just do this for laughs and, you know, I don't know if they took it seriously or whatever

''It's actually good for the calves.''

And Mariah was thrilled that Rihanna shared one of her pictures as she was wearing heels from the 'Work' hitmaker's FENTxPuma collection.

She said: ''I love her. I think she's beautiful and amazing. I love her shoes. I love those Pumas!''