The Welsh singer, 31, revealed the news live on stage at Gay Pride in Birmingham, cradling her stomach as she shared her happiness with the crowds.
The baby will be the first for Charlotte and partner Jonathan Powell, but she is already mum to Ruby, nine, and eight-year-old Dexter, from her relationship with rugby player Gavin Henson, before the pair ended their engagement in May 2010.
Charlotte and musician Jonathan began dating later that year, and she's said in the past that she wouldn't rule out starting a family with her new beau.
'I'm really happy with my dude. He's lush, he's so smart and he really looks after me,' she stated previously in a rare interview about her personal life.
'I don't know. I'd never rule out anything. Never say never!'
Charlotte has revealed that she's expecting her third baby
Classical performer Charlotte shot to fame at the age of just 11, getting her big break after singing Andrew Lloyd Webber's 'Pie Jesu' over the phone during an episode of This Morning in 1997.
She subsequently appeared on ITV's Big, Big Talent Show, and released her first album, Voice of an Angel, the following year.
Speaking to the Guardian in 2012, the star explained that motherhood had prompted her to see the world differently: 'I've always been mature, but I think it's made me more emotional and responsible. And more caring. You want to be as safe as you can possibly be, so that when you go this world is OK, bearable, for your children to grow up in.'
Of her relationship with ex Gavin, she added: 'We've got a good relationship. It works pretty well when you've got two people who want the best for their children and can leave other baggage behind.'