The TV presenter, 36, shared an Instagram photo on 2 January of herself and her three-year-old son both donning blue and white swimwear.
She and Chester were sat on the edge of the pool in a diving position and looking out onto a beautiful sunny scene.
Willoughby captioned the shot with a string of blue emojis and wrote: ”🦋💎🌊🐳🐬💙... all the blues x.”
The mum didn’t share where she is on holiday, but fans all agreed the snap was beautiful.
“Wow where is that, the scene is amazing - you and Chester fit in so beautifully with the colours haha lovely family time,” one person wrote.
Another commented: “That’s the life! Not sure where you are but it looks stunning. Chester is so tall, what a lovely mummy-son shot.”
Willoughby also shared another photo of her underwater on New Year’s Eve, writing: “Going out of 2017 in style...”
As well as Chester, she is also mum to Harry, eight, and Belle, six, with her husband Daniel Baldwin.