Sean announced his exciting news on Twitter today (23 January), admitting that he feels "emotional" about his daughter's arrival into the world.
The news has come just one day after Sean's 5ive bandmate Scott Robinson revealed that his wife Kerry gave birth to twin girls last Friday.
Sean said: "My little girl was born last week. Words can't describe how happy and emotional I felt and feel. #Love #Proud #Family."
Sean's fellow Big Reunion star Michelle Heaton, who is pregnant with her second child, replied: "@SeanConlonMusic awwww congratulations guys! Bet she's as beautiful as her mummy xxx."
Although 5ive reformed last year for The Big Reunion, Sean and his wife - who prefers not to be named - like to lead a private life.
Last week, Ritchie Neville let slip that Sean was about to become a dad, as Sean had not even announced it himself!
More celebrities who have welcomed babies in 2014:
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