Bungie, the developer of the hugely popular Halo series, is to part company with owner Microsoft.
In a statement, the two firms said they would "forge a new long-term partnership" based around new games.
The move will surprise many in the games industry, despite rumours about a split in recent weeks.
Bungie is now a privately held company in which Microsoft holds a minority stake. Recent release Halo 3 made $300m (£150m) in its first week on Sale
The Halo series has sold more than 18 million copies worldwide since the first game was launched in 2001. Halo 3 has become the fastest selling game of all time following its launch on 25 September, with more than three million copies already sold.