After months of rumours and speculation, Microsoft finally let the Windows 8 upgrade cat out of the bag. Formerly known internally as Windows Blue, Windows 8.1 will be a free upgrade to Windows 8 and Windows RT that will be available from the Windows home screen when it is officially released later this year.

Tami Reller, CFO and CMO of Microsoft’s Windows division, revealed the coming Windows 8 update package as part of JP Morgan’s Technology, Media and Telecom Conference. No official release date was announced but a public preview build would be made available starting June 26th to coincide with the Build 2013 conference.

Windows 8.1 is expected to bring a plethora of new features to Windows 8. These include a new side-by-side app view and Internet Explorer 11 (which is a great idea seeing as Microsoft has only just released IE10 for Windows 7). Additional new apps include a new movie maker software called Movie Moments and a new calculator app called Calculate. The upgrade will include a number of cosmetic updates as well.

Reller’s speech at the JP Morgan conference also hinted that Windows RT 8.1 would be able to work on tablets smaller than 10 inches. Now that would be something a bit more noteworthy than just an upgrade.