Louis Tomlinson is said to be "made up" at news his mother is expecting twins.
The One Direction heart throb already has four sisters - Lottie, Felicite and twins Phoebe and Daisy - and he is reportedly delighted Johanna Poulston is due to give birth next year.
An insider told The Sun newspaper: "It's brilliant news. Everyone is made up, especially Louis who already adores his sisters."
The star's midwife mother has been with her partner Daniel Deakin for two years, who she met after splitting from Max Tomlinson while Louis was auditioning for 'The X Factor' UK in 2010.
A spokesman noted: "Louis and his family do not wish to comment as it is a private matter."
Johanna has spoken in the past about how proud she is of the 'Best Song Ever' hitmaker, while explaining he does everything he can to look after his sisters.
She previously said: "He's very caring and protective of me and his sisters. He sends money for their school trips and posts them Topshop vouchers.
"He does lots of little things for me - he even paid for me to have a gardener because he wanted to make my life easier ... He rarely gets to come home, though he loves it when he does.
"He misses his sisters and his old bedroom, which we've kept exactly the same. He says sleeping in it gives him a sense of calm."