Some awesome information was revealed during the PlayStation Experience 2016 Day 1 stream which revealed more information about Uncharted: Lost Legacy.
It was first revealed that it will be set after Uncharted 4, and it was originally going to be a DLC, but changed to a standalone game in the middle of the development. It will also be longer than The Last Of Us: Left Behind and shorter than Uncharted 4. Was said to be “in the middle” so it could be up to 6 hours long.
What was shown at PSX was the beginning of the standalone, and is going to give much more backstory on Nadine and Chloe’s characters.