Possible The Wolverine spoilers ahead, folks. Just a warning so as not to ruin what could be a cool aspect of the story.....
Recently, Bryan Singer was discussing the future of the X-men franchise, and hinted at the possible "connectivity" of a shared mutant universe. We saw a little bit of it when Hugh Jackman's Wolverine turned up in X-men: First Class, so it would seem to make sense that The Wolverine would also feature characters from other films. With Patrick Stewart recently stating that he would be back in some way as Professor Charles Xavier, now a rumor has surfaced that Famke Janssen will reprise her role as Jean Grey in The Wolverine.
We Got This Covered notes a source who revealed Janssen flew to Australia last week to shoot a cameo. Fans may recall that Wolverine killed Jean while she was possessed by the Dark Phoenix at the end of X-men: The Last Stand, but since The Wolverine is a prequel of sorts, she could turn up and have it not be a total retcon. Er, a "retcon" is short for retroactive continuity. Basically it's when a creator changes something from a character's past rather than dealing with it. It's comic book fanboy nerd-speak.
Take this with a grain of salt, of course, but I don't think she'll be the only X-man we see in The Wolverine. I also believe we'll see plenty more in X-men: Days of Future Past, which has a time-hopping storyline that could be a way of wiping the slate clean and resetting the franchise. One can hope. The Wolverine opens on July 26th 2013.