"The Flash" has one episode left and the season 1 finale is shaping up to be the most climactic event in the television series thus far.

According to a report from the Inquisitr, actor Grant Gustin, who plays Barry Allen a.k.a. the Flash in the series, described the finale episode as a "heartbreaking" and deeply emotional episode. 

Gustin also hinted that the events in the finale will change the overall tone of the series moving forward.  

The promotional trailer for the episode reveals Barry facing off against Eobard Thawne a.k.a. Dr. Harrison Wells or Reverse-Flash (Tom Cavanagh). Barry asks why Eobard killed the former's mother and the latter simply replies that it was because he hates Barry Allen. 

One of the main themes that the trailer gives away is that Barry needs to travel back in time and alter the course of history. It is hinted that by saving his mother's life, he might be able to stop Reverse-Flash but this would also mean that Barry as the Flash would no longer exist since Dr. Wells wouldn't have been able to found S.T.A.R. labs. 

The trailer shows Wells attempting to use the particle accelerator to defeat Barry and possibly erase him from existence. However, two special guest stars from the upcoming "Arrow" and "Flash" spin-off series "Legends of Tomorrow" will be coming in to help Barry in his final fight against Wells. 

Both Ronnie Raymond (Robbie Amell) and Dr. Martin Stein (Victor Garber) will be in the episode. Actress Ciara Renee also posted via Twitter a message hinting that Hawkgirl will be making an appearance as well, and she might be the one to deal with the meta-humans responsible for helping Wells get out of prison. 

According to a report from E! Online, Eddie Thawne (Rick Cosnet) might finally stumble down the dark path in this season 1 finale. Previous episodes revealed that Wells is, in fact, the descendant of Eddie and perhaps the defeat of Wells here would provoke Eddie into becoming a villain as well. 

"The Flash" season 1 finale, "Fast Enough," airs May 19 on the CW. To watch the finale online tonight, go to the CW website.