Creator Masahiro Sakurai took to Twitter to confirm the news today. He said (via Google translation): "In Nintendo Direct delivery of 23:00, June 11, New video of "Smash Bros." will be unveiled for the first time. Simultaneous world, here for the first time! Do not miss." You can watch it from 3pm UK time.
Nintendo president Satoru Iwata recently said Nintendo would use its E3 webcast to discuss "new Smash Bros., 3D Mario game, Mario Kart and other Wii U titles".
Sakurai is serving as producer on the new Smash Bros. game, which is a Wii U/3DS crossover in development at Namco Bandai
Official Nintendo Magazine associate editor Matthew Castle recently labelled the title his most anticipated game of E3, writing:
"Sakurai says he wants the 3DS version to be a more personalised, individual experience that feeds into a competitive public space on Wii U, and that would certainly play to the strengths of both systems.
"He's also tidying up online play - great news for those us that spent months of our lives hanging out in Brawl's notoriously flaky pre-match lobby.
"I'm more concerned about how much of the game we'll actually see. Every promise Iwata makes about showing the game at E3 is met with a cautious 'wait and see' from Sakurai."