Charlotte Church and her two children were almost killed by a deadly gas leak at her new home.
Charlotte was terrified when she found out what had been happening and said she feels lucky to be alive.
The 24-year-old singer - who has three-year-old daughter Ruby and son Dexter, two, with ex-fiance Gavin Henson - had been suffering from headaches and only became aware she was being poisoned when her concerned grandfather suggested she install a carbon monoxide detector at the £1.3 million mansion in South Wales.
A source said: "Charlotte was terrified when she found out what had been happening and said she feels lucky to be alive. She had been complaining of headaches for weeks but had no idea why.
"Then her granddad suspected carbon monoxide could be the reason and installed a detector to find out. Thanks to him, both Charl and the kids are fine."
Friends believe Charlotte - who moved to the five-bedroom house in July after splitting for rugby star Gavin - managed to escape unharmed because the house is so big.
The source added to Closer magazine: "She had no idea that the boiler was playing up. When she heard the carbon monoxide alarm go off, she called in a plumber, who said her granddad saved her life.
"She is probably lucky that the house is so big and airy and the boiler is a long way from the living areas. But she knows she's had a lucky escape."