The singer, 38, posted the picture of his pregnant wife posing in their LA home with the caption 'My two girls!'
Ayda, 32, is photographed lifting her T-shirt to reveal her growing belly and glowing with happiness.
And despite her growing stomach, she still looks remarkably toned.
The couple's first baby is due in September.
Robbie announced the news back in March that he and his wife of almost two years are expecting a baby. Less than a week later, they revealed she is a girl. He has previously said he was 'terrified' of fatherhood, although Ayda was keen to start a family.
Williams announced that he is to become a father in typically comic fashion, writing on his website in March: 'Hey friendlies, I've been keeping a secret from you all. Me and Ayda are going to be a Mummy and Daddy this year!!!!!!!!
He added: "We had sex! It works!
"We've seen scans and cried... looked at babies in commercials and teared up... the nursery is already planned.
"Basically I'm in love with a little person growing in mummy's belly... and can't wait to be a daddy. Crying now.
'Much love, much joy. Roberto, Mum and Little Bump. xxx'
Doesn't Ayda look blooming?