The Saturdays star's husband Ben announced their exciting news yesterday (2 February) and the couple have since been inundated with messages of congratulations.
Taking to Twitter herself, the mum-of-two told her followers last night just how smitten she is with the latest addition to their family.
She said: "So so in love with our little son Tadhg. Thank you for all the lovely messages xx."
Singer Una, who is also mum to daughter Aoife Belle, announced her pregnancy in September before embarking on an energetic tour across the UK and Ireland with her Saturdays bandmates.
Following their news of Tadhg's arrival yesterday, the girls were quick to send messages of congrats to Ben and Una too!
Rochelle Humes, who is mum to daughter Alaia-Mai, said: "Tadhg John Foden has arrived. So so excited to have some Aunty Roch cuddles. Well done to my @UnaTheSats @ben_foden #lockupyourdaughters x."
Vanessa White, meanwhile, added: "Congratulations @UnaTheSats and @ben_foden on baby Tadgh!!! I can't wait to meet this little man!"
Frankie Bridge, who is pregnant with her second baby, tweeted the couple, saying: "@ben_foden @UnaTheSats can't wait to meet the little man! Parker's excited to have another boy to play with! Well done Una!"
And Mollie King joked: "So so happy for you @UnaTheSats & @ben_foden!!! …Watch out Brad Pitt there's a new heartthrob in town!!"
Announcing their news, rugby player Ben had previously told fans that his son takes after his mummy.
Yesterday afternoon, he excitedly tweeted: "Tadhg John Foden has been born! Mum and baby are both amazing and healthy. He has a full head of hair and his mummy's lips! #babybenuna."
Congrats again, guys!
Celebrities who have announced pregnancies in 2015:
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