Update (May 31)
The logo over at Larian's website has updated to include tentacles.
Original (May 30)
Late last year, rumors began to circulate that maybe, just maybe, Larian Studios of Divinity: Original Sin fame were working on Baldur's Gate III. However, Larian quickly denied these rumors. The speculation of the moment then redirected, thinking maybe inXile or Beamdog were instead working on the project, only for the murmurs to eventually die down as we collectively waited for new information.
However, here approaching the eve of E3 2019, Larian is now teasing a new project on their website. At the time of writing, the page simply shows a giant Roman numeral III in the dead center. Needless to say, excitement about the potential of a Larian-developed followup to the CRPG classics is resurfacing, and it's obviously something we're pretty stoked about.
While Larian has recently announced a series spin-off in Divinity: Fallen Heroes, that project is actually headed up by Danish studio Logic Artists, leaving this tease to attribute to Larian itself. Even if this new image is actually instead a tease for a Divinity: Original Sin III, either way it's something we're going to keep a close eye on. We hope to hear more in the coming weeks.