"It's really important to us that Faerun feels unique and is more true to the classic high-fantasy setting," says producer Fernando Paiz. Whereas Eberron featured elements of fantasy-tech and magicpunk, the Forgotten Realms is one of the more iconic and traditional high fantasy settings around. As such, Turbine says, it has collaborated closely with Wizards of the Coast to ensure the authenticity of the expansion experience.
So what is the link between these two different realms? In a word, Lolth, the drow spider-queen goddess who is powerful enough to connect the worlds. Turbine remains mum on the specifics, though, so you'll have to check out the expansion to see for yourself.
[Source: Turbine press release]