Lensvid posted this video interview with Stephan Daniel from Leica:
Stephan Daniel confirmed that they started talking with Panasonic about 2.5 years ago before Sigma joined the partnership (called the L-mount alliance – a name which we are hoping will change in the future), from our
talk with Mr. Kazuto Yamaki, the CEO of Sigma it seems that Panasonic was in contact with both Leica and Sigma separately before the actual alliance was formed and each company didn’t know about the other until a later stage.