Facebook owned Instagram has incorporated another facebook owned company WhatsApp as one of the new sharing option within the app. You can already share your Instagram posts on Facebook and Messenger.
Now Instagram has also included WhatsApp as the new sharing option apart from Facebook and Messenger App. You will now be able to share your Instagram posts on WhatsApp via Instagram App.
— Windows Club (@WindowsClubBr) January 4, 2017
The company is not pushing out any update to the Instagram app in the Windows Store. The option will be added via a Server Update. The option is being added gradually to the Instagram app on all platforms.
If you have not received the WhatsApp as the new Sharing option, please close and re open your Instagram app and you will be able to see WhatsApp as the new Sharing option apart from Facebook and Messenger.
Earlier Facebook had added Instagram Stories and other features via a Server Update to the Instagram app. The company has released all the new features to its App on All platforms simultaneously.