Shem Davies was also 14 when Tia was born, who celebrated her 15th birthday in hospital after giving birth to her baby girl - Gracie.
Shem, who was mistaken by maternity nurses as Gracie's father, said
: "It is an absolute joy to see Gracie thriving. I'm incredibly proud of Tia. She'll be a brilliant mum. At first I wasn't overly pleased that she was pregnant but I soon got over that. Now it's all about being positive."
Gracie's father is 15-year-old Jordan Williams, who Tia has been dating for 18 months. He said: "I'm captain of the school rugby team and that's like having 14 kids."
Shem split up with Tia's mother - Kelly - just three months after she was born. The unemployed grandfather also has a nine-month-old son with his current girlfriend - Robyn Thomas.
He added: "One minute Tia's a baby, the next she's pregnant. I could have yelled at her, but what's the point? I know how hard it's going to be for them because I was in their shoes at the same age. I didn't handle it very well when I became a dad at 14. I wasn't able to cope with it and I ran away."
Meanwhile, Tia's mother - Kelly - said
: "My worst nightmare has always been that Tia would repeat my mistake and get pregnant young. I always lectured her about contraception."
Weighing a mere 2lbs, Baby Gracie was born by Cesarean section
in the Princess of Wales Hospital in Bridgend, South Wales. Although she has gained enough weight to depart the hospital in several weeks, Gracie is currently being kept in an incubator.
According to recent figures
, the United Kingdom has the second-highest teenage birth rate
in the developed world. There were 38,259 teenage pregnancies in 2009 alone, although 50% of the mothers had abortions.