Charlotte Church thought she was going to die when she began her gruelling weight-loss regime.
The curvy 23-year-old singer is feeling "sexy again" after losing 12kg in two months, but friends say her new body didn't come easily.
An insider said: "Charlotte works out five days a week and reckons it's the most intensive workout she's ever followed.
"The first time, she told us: 'I thought I was going to die!', but she's really stuck to it and reaped the rewards. Charlotte is really feeling sexy again."
Charlotte has struggled to lose the weight she put on while pregnant with her two children, Ruby, two, and Dexter, 13 months.
Now, thanks to a training regime devised by her rugby player boyfriend Gavin Henson, she has lost three dress sizes and is even considering making her own workout DVD.
The source told Britain's Star magazine: "She's feeling great and if she can lose another dress size, she wants to do a workout video.
"She wants to keep her curves though. She hates the idea of becoming stick-thin."