The celebrity chef posted the snap on December 30 showing the adorable bub sucking his thumb.
'River found the glory of the Thumb = good times, gave me years of pleasure. Big love folks joxx,' he wrote.
The post has been liked over 30,000 times, with many commenting on how cute the newest addition to the Oliver tribe is.
‘That little cute mouth!’ one fan wrote.
Another added: ‘You are truly blessed with your beautiful family.’
Jamie took to Instagram on August 8 to reveal the birth of River. 'Everyone in the Oliver family is very surprised and beyond happy,' he wrong alongside the sweet snap.
'He arrived safely, mum was really, really amazing, unbelievably composed, natural birth and my two eldest girls got to come in at the very end as the baby was born which was amazing to witness.'
Jools also shared a picture of the bub on Instagram, saying she was 'very proud' of the couple's teenage daughters Poppy Honey and Daisy Boo who cut the umbilical cord at the end of her labour.
This article originally appeared on Practical Parenting.