The Surface Phone is without a doubt one of the most eagerly anticipated products ever developed by Microsoft, and one of the reasons is the simple fact that it could keep the company’s mobile platform alive.

And while there’s a good chance that a future Microsoft mobile device, no matter its form factor, wouldn’t be powered by Windows 10 Mobile, one of the features that many Windows phone diehard fans are drooling after is support for a pen.

Microsoft’s Surface Pen has been around for many years already, but the company has never shown any interest in bringing it to the mobile platform officially, though this would have positioned the company as a direct rival to Samsung and its Note series.

But even though such a product never launched, it doesn’t mean it didn’t exist. Known as Hapanero, a Lumia 950 with support for the Surface Pen was the closest thing Microsoft could get to competing against the Samsung Galaxy Note phablet, with the device presented by the company itself during the Build developer conference in 2015.

Surface Pen on Windows phones

A video that made the rounds today shows a rare demo with this prototype, revealing how a Windows phone with support for the Surface Pen would have worked.

As WL notes, a stylus was supposed to let users open apps, scroll, and even type on the keyboard, more or less mimicking the legacy touch input. Without a doubt, however, Microsoft had in mind much more advanced functionality for Surface Pen support, some of which is currently available in Windows 10 on PCs, like drawing and annotations.

Rumor has it that Microsoft planned two different versions of the device with 1080p and 1440p screens, while specs would have been similar to the ones of Lumia 950, including a Snapdragon 810 processor, 4GB RAM, 32GB storage, and 20-megapixel main camera.