Katherine Heigl knew she had abs ''buried under her belly somewhere.''

The 39-year-old actress set tongues wagging after she shared a series of photographs on her Instagram account of her post-baby body - 14 months after her son Joshua Jr was born - and has admitted she decided to get her bottom into gear after booking a beach holiday and signing up to a new job which will start in April.

Alongside the photograph, she wrote: ''It's been almost 14 months since Joshua Jr was born and it has taken me about that long to really get back in shape. The first pic was taken one month after he was born. The second pic was taken almost a full year later and the last pic was taken this weekend. I wish I had a few from in between the first and second so you could really see how slow my progress was but alas...I was busy covering it all up those months, not posing in my unders!

''Anyway, I have a beach vacation coming up, a new job I start filming in April and my deep desire to feel fit, strong and sexy propelling me forward the last two months to finally loose the last of my baby weight and do a deep dive search for the ab muscles I knew were buried under that belly somewhere!''

The blonde beauty has been married to Josh Kelly for 11 years and the pair have three children together - two of which are adopted.

And Katherine has opened up about her family's history with adoption in the past and said it ''felt right'' for the couple to adopt.

Speaking to The Daily Mail before the adoption of her first child in 2012, she said: ''My husband and I wanted to have a baby, and to us it didn't matter how it happened. Adoption has been a part of my life and a part of my family, so it was how I wanted to start. It felt natural and right to me.''