Tomb Raider: Underworld developer Crystal Dynamics has revealed the truth behind the controversial Xbox 360 exclusive downloadable content deal that has left PS3 and PC gamers out in the cold.

Speaking to in an interview to be published later today, creative director Eric Lindstrom said that the 360-exclusive DLC isn't content cut from the main game but "especially made", and only came about after Microsoft approached the developer.

Earlier this month publisher Eidos announced plans for two brand new chapters providing up to six hours of additional gameplay, the first of which will be available to download before the end of the year.

Tomb Raider: Underworld - Beneath the Ashes, which will be available this Christmas, takes place after the Underworld story has finished and will feature a new environment to explore, additional secrets to unlock and different enemies to fight. Tomb Raider: Underworld - Lara's Shadow, planned for early 2009, will introduce players to a new playable character.

Lindstrom explained that the new chapters are "not part of the main game" and that Microsoft approached them to make the extra content.

"To be honest, it completely came down in the other way," he said. "We were approached by Microsoft, who asked us if we could make some downloadable content for them. It was a great opportunity, it was a great deal and we're happy to do it. The DLC that we're making for Microsoft is especially made. It's not part of the main game that we saved - we put all the game out there that we were going to put out there. Now we're going to the trouble of adding on spaces where they logically make sense, telling parts of the story."

The 360-exclusive Tomb Raider: Underworld DLC is the latest in a string of deals secured by Microsoft for its console. 360-exclusive GTA IV and Fallout 3 DLC is inbound, a strategy that has drawn criticism from some quarters for being unfair to owners of other gaming platforms.

Lindstrom added: "Whenever you make a story like Tomb Raider, you're only telling part of it. We come up with all these logical motivations and rationale behind the scenes that inform what story the player understands - but there are all kinds of details that never see the light of day. Rather than making up a bunch of new stuff, there's plenty out there that's never been told - that was never really going to be told - but that we now have a chance to do it, and we're doing it. So it really wasn't about, 'let's make these levels and only give them to Microsoft'. It kinda came around the other way."

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