Xbox boss Phil Spencer has confirmed to Eurogamer that Microsoft's controversial exclusivity deal for Rise of the Tomb Raider "has a duration".

However, he declined to confirm how long that duration is set for.

Last night, during its Gamescom press conference, Microsoft and Square Enix made the surprise announcement that Rise of the Tomb Raider would launch holiday 2015 exclusively on Xbox. That, Spencer confirmed, means Xbox One and Xbox 360.

But the wording of its statement caused some to wonder whether the game would eventually launch on other platforms. Spencer wouldn't speak for Square Enix on this, but did compare the deal to that it had for Xbox One games Dead Rising and Ryse, which will also launch on PC.

Spencer's comments confirm Square Enix, owner of Tomb Raider developer Crystal Dynamics, is free to do whatever it wants with the game and the franchise after the exclusivity deal ends, including releasing it on other platforms.

Here's our conversation:

"When people want me to say, can you tell us when or if it's coming to other platforms, it's not my job," Spencer told Eurogamer. "My job is not to talk about games I don't own. I have a certain relationship on this version of Tomb Raider, which we announced, and I feel really good about our long term relationship with Crystal and Square.

"I get the reaction I see. If I'm a PlayStation person all of a sudden I feel like, the franchise has gone. I didn't buy the IP. I didn't buy the studio. It's not mine. Where this thing will go over time, just like Dead Rising or Ryse, we'll see what happens with the game. I don't own every iteration of Tomb Raider.

"I don't own them building Tomb Raider on other platforms. I can't talk about the franchise that way. I can talk about the deal I have."

So, what, exactly, is that deal?

"I have Tomb Raider shipping next holiday exclusively on Xbox. It is Xbox 360 and Xbox One. I'm not trying to fake anybody out in terms of where this thing is. What they do with the franchise in the long run is not mine. I don't control it. So all I can talk about is the deal I have. I don't know where else Tomb Raider goes."

Is there a time limit on the exclusivity period?

"Yes, the deal has a duration. I didn't buy it. I don't own the franchise."

Can you tell us how long the duration is?

"No. It's not because I'm trying to be a headfake on anybody. It's a deal between us and the partner. People ask me how much did we pay. There are certain things I'm just not going to talk about because it's a business deal between us and them. Obviously the deal does have a duration. I didn't buy the IP in perpetuity."

Angry gamers have directed many of their comments towards Square Enix, accusing the publisher of selling out and alienating their PlayStation and PC owning customers.

"Our friends at Microsoft have always seen huge potential in Tomb Raider and have believed in our vision since our first unveil with them on their stage at E3 2011," wrote Darrell Gallagher on the Tomb Raider tumblr. "We know they will get behind this game more than any support we have had from them in the past - we believe this will be a step to really forging the Tomb Raider brand as one of the biggest in gaming, with the help, belief and backing of a major partner like Microsoft."