'CSI' Reunion: Marg Helgenberger Shares Willows/Grissom Picture On Twitter! Which Characters Are Returning In 'Crime Scene Investigation' Series Finale? [PHOTOS]

It really looks like 'CSI: Crime Scene Investigation' plans on going out with a huge bang!

The long-running CBS show will end with a two-hour TV movie and everyone is returning for the series finale.

'CSI' is already shooting for the finale, and the cast couldn't seem to stop themselves from posting amusing behind-the-scenes photos and adorable reunions.

Marg Helgenberger, who plays Catherine Willows, has just shared a picture on Twitter showing the actress with longtime 'CSI' costar William Petersen on the set, while Jorja Fox and Paul Guilfoyle conversed in the background. She added the caption, "#Grillows with Jorja & Paul backing us up. #CSI4EVER!"

William Petersen played Gil Grissom in the first season until 2009, but has appeared in a few special episodes. Marg Helgenberger also starred in Season One and stayed with 'CSI' until the thirteenth season.

Helgenberger also posted a Twitter photo showing her, Petersen and Paul Guilfoyle with current 'CSI' regulars Eric Szmanda and Jorja Fox. The caption read, "#OGCSI Great fun today with this gang!"

The 'CSI' series finale will not only see the return of William Petersen, Marg Helgenberger and Paul Guilfoyle. According to TV Line, Melissa Clarke is set to appear once again as the dominatrix Lady Heather.

But will Nick Stokes return for the 'CSI' finale?

Unfortunately, George Eads will not reprise his role as the demoted assistant night supervisor. TV Line reported that the actor has decided not to join the series finale and did not offer an explanation.

George Eads' decision to sit out the 'CSI' series finale was a surprise to show creator Anthony E. Zuiker, who had to remove Nick Stokes from the finished script. Luckily, it wasn't a huge change, since the character was sent to San Diego in the last season.

The 'CSI' two-hour finale will air on CBS on September 27.

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