The developer ignited speculation on the internet that it was about to reveal the long-anticipated new Half-Life 2 episode after sending out a mysterious email.
In the message, the studio said that a planned Portal 2 event at E3 would be replaced with a "surprise".
A Half: Life fan subsequently asked Newell whether the announcement would be Episode 3 via the HalfLife2.net forum.
However, the Valve boss replied that the surprise unveiling "isn't Ep 3".
Valve will definitely be demonstrating Portal 2 at E3, but the other announcement is yet to be revealed.