Johanna Poulston and her fiance Daniel Deakin welcomed a boy, Ernest Rupert Atholl Deakin, and girl called Doris Poppet Deakin, Tomlinson's spokesman has confirmed.
The representative added, "Daniel and Johanna would like to thank Barnsley hospital, their special care unit, the Embrace team and Jessops special care unit. All the family are delighted."
Tomlinson already has four younger half-sisters, Charlotte and Felicite and twins Phoebe and Daisy.
Poulston has been dating Deakin for two years. She split from her famous son's father Mark Tomlinson when the 22 year old was auditioning for The X Factor U.K. in 2010.