The former Catatonia singer and her new son - who she has with her boyfriend-and-manager Steve Abbott - are both "doing very well", despite going into labour eight weeks prematurely.
Cerys - who delivered her son on Monday (23.11.09) - said: "How happy I am to let you know that our baby boy was born on Monday 23, eight weeks earlier than expected.
"We are doing very well and excited now to share this happy news with you.
"What an amazing surprise. Love always, Cerys and Steve."
Cerys went into labour just days after co-presenting the charity telethon `Children In Need`, at the Wales Millennium Centre in Cardiff on Friday (20.11.09).
The baby - who has not yet been named - is the first child for the couple.
The 40-year-old singer already has two children - daughter Glenys Pearl and son Johnny Tupelo Jones - with her ex-husband, American music producer Seth Riddle, while Steve, 49, has two children with his ex-wife Deborah.
Cerys and Steve originally kept news of the pregnancy secret, following concerns there could be complications with the pregnancy because of her age.
At the time a friend said: "Cerys and Steve are delighted - they could not be happier. They wanted to keep the situation under wraps until they were certain everything was going smoothly."