Back at Mobile World Congress 2016, HP introduced the Elite x3, the most powerful Windows phone ever. It was meant to be a three-in-one PC, using Microsoft's Continuum feature to allow you to also use it as a laptop or a desktop. It shipped that fall, and the Elite x3 ended up being the second to last major Windows phone release.
But that doesn't mean that HP wasn't working on more Windows phones; indeed, it was. It even showed off a new one at Mobile World Congress the next year. It was only on display though, and HP never commented on it. Images of that device leaked recently, as spotted by Windows Latest. It's not exactly a successor to the Elite x3 though.
As shown in the watermarks, this device would have been called the Pro x3, and some of the specs leaked in late 2017. It would have reportedly had a Snapdragon 820 chipset, 3GB RAM, and 32GB of internal storage. The Elite x3 had shipped with a Snapdragon 820, 4GB RAM, and 64GB of storage, and it also had a 1440p OLED display. It's possible that this lower-end unit might have had something like a Full HD LCD panel. You can also see from the images that the Pro x3 lacks the Elite x3's front-facing B&O speakers.
Elite is HP's premium business brand, while Pro is typically for lower-end products (like EliteBooks and ProBooks). Of course, Windows phone is dead and none of this matters, but it can always be fun to take a quick look back at what could have been.