The 38-year-old Take That star took a picture of Ayda Field lifting her shirt to reveal the baby bump in their Los Angeles home, writing "My two girls!", reported Ace Showbiz.
Field is due to give birth in September. They announced the pregnancy in March, almost two years after they got married.
"Hey friendlies, I've been keeping a secret from you all," Williams gushed. "Me and Ayda are going to be a Mummy and Daddy this year. We've seen scans and cried, looked at babies in commercials and teared up. The nursery is already planned," Williams had written.
The couple will reportedly name the baby girl Roberta after her father but they were considering Genevieve and Alice as well.
For the nursery, they have decorated it with items from Petit Tresor such as custom-designed sleigh cribs and Notte Fatata.
