The Flash Season 3 became the show's darkest year, but the fourth season is all about bringing back the light. Producers of the show have stressed as early as San Diego Comic-Con about this season's new tone.

"We're also trying to lighten the tone this year. Last year was pretty dark, we're going to try to get back to the jokes."

Every season we've met a new Harrison Wells from the Multiverse. While Season 4 will still feature Earth-2 Harry, we'll most likely meet a new one later in the year.

Tom Cavanagh teased back at Comic-Con that they're exploring what new Harrison they will use.

"We're just gonna start there, with [Harry], and see as we progress toward the big season arcs – I don't know what you guys know about the main villain and stuff – but we're going to, around that time, see what other versions of Wells are available.

He said, politically correctly, without giving hardly anything away...Like I say, there are all these different Earths we created, and there are all these different Wells to pick from, and so we pick from them."

Be sure to let us know in the comments what type of Harrison you'd like to see!

One of the fan-favorites from the past season was Jessica Camacho's Gypsy, a bounty hunter from Earth-19. She'll be a recurring guest-star this season as she'll keep bonding with Vibe.

However, is Vibe ready to meet her father? He better be because Danny Trejo is set to recur as Breacher, who is also a bounty hunter. Breacher is described as an imposing man who will do anything to "prevent any inter-dimensional traveler from threatening life on his planet – especially his daughter's."

Will daddy approve of his daughter's man? Tune in on Tuesday nights to find out!

Expecting an evil speedster in The Flash Season 4? Forget about it because The Flash Season 4 is going a different route this year with their big bad. Neil Sandilands (The 100) is set to play DC villain Clifford DeVoe a.k.a. the Thinker.

After several hints in the third season, the CW drama is officially bringing him in as Barry new foe. WBTV describes him like this:

"A metahuman with a mega mind who embarks on a season-long battle with The Flash that pits the "fastest man alive" against the "fastest mind alive."

A true genius, he's devised an intricate plan to fix all that he deems wrong with humanity."

But DeVoe won't be working alone, which brings us to our next point...

While we don't see many of them on the show, we're getting another female baddie this year. Kim Engelbrecht (Dominion) will be playing DeVoe's right hand, the Mechanic. She will recur alongside the Thinker throughout the season. The way WBTV describes her is like this:

"A highly intelligent engineer who designs devices for DeVoe.

As DeVoe's right hand, she's the truest of true believers who'll stop at nothing to help him implement his plan to fix humanity."

While Barry and Iris will always be the show's power couple, there's a lot of romances growing this season. At San Diego Comic-Con, Jesse L. Martin teased the growth of Joe West and Cecile Horton's relationship in the coming season.

"It's going to progress. That's really all I can say. She's going to be around, so we'll see what happens."

With Gypsy sticking around on Earth-1, expect their relationship to evolve too. In addition to that, Andrew Kreisberg teased recently that we'll see some evolution in Wally West and Jesse Quick's romance.

After having seen a lot of villainous meta-humans in the past seasons, it's time for some good ones. Hartley Sawyer will be recurring as DC Comics' Ralph Dibny a.k.a. the Elongated Man!

Ralph can stretch his body to superhuman length and sizes while working as a private investigator. According to CW, Ralph will help Team Flash solve one of Central City's greatest mysteries.

While we'll see plenty of new faces this season, one familiar face isn't coming back. Tom Felton, who joined The Flash Season 3 as Julian Albert, is confirmed to not be appearing in the new season as of right now.

Even though he formed a bond with Caitlin Snow during her rough Killer Frost period, Felton's character won't be seen. Fingers crossed for a guest spot in the second half of The Flash Season 4? Speaking of Caitlin...

Danielle Panabaker has been cryptic about what we can expect of Caitlin as well as Killer Frost in The Flash Season 4. At Comic-Con, the actress assured fans of both sides of her character that The Flash Season 4 will be good for Caitlin.

"Those who love Caitlin Snow won't be disappointed and those who love Killer Frost won't be disappointed."

Only time will tell what that exactly means, but be sure to tune in if you're a Caitlin/Killer Frost fan!

If you're an Iris West fan, then get ready to see more of her this season. In Barry's absence, Iris will be taking over as the leader of Team Flash, for the sake of Central City, but also while her heart heals.

In a Comic-Con interview, Candice Patton talked about Iris's new role while she deals with Barry's absence.

"She's had to sort of step into the role that Barry left. It's a way of distracting herself too. She's obviously depressed and sad that Barry's gone, not sure when he's going to come back, so it's a good distraction for her to be the leader.

She deals with that in her own way, I think you'll see a very different Iris in Season 4; she's almost hardened and a little more pessimistic, and is kind of like, we gotta move forward, we gotta just keep moving. We don't know if Barry's coming back, we can't deal with that, all we can deal with is protecting the city."

The DC TV shows have a lot of butt-kicking ladies, and this year another one is coming to The CW. Katee Sackhoff (Battlestar Galactica) will play the villainous DC character Blacksmith, who will recur in The Flash Season 4.

As one of the iconic Rogues from the comics, The CW describes their take on Blacksmith as follows:

"Amunet Black a.k.a. Blacksmith, a steely and badass boss of an underground black market for supervillains.

Amunet uses every means possible, including the long list of metahumans under her thumb, to ensure her illicit enterprise thrives."

She'll make her debut in episode 5 which will be a female centric episode. Speaking of that episode, that brings us to another exciting thing in The Flash Season 4...

In episode 5, titled "Girls Night Out", we'll see Arrow's Felicity Smoak (Emily Bett Rickards) guest-star for a, as the title says it, girls night out. Supposedly we'll see several female characters hanging out in 4.05, including Sackhoff's Blacksmith.

Could it maybe be for a bachelorette party for a certain Ms. West? More on that later.

The Flash Season 3 ended with our hero entering the Speed Force, but the show is called The Flash after all, so of course, Barry is getting out. However, expect some changes on our dear Mr. Allen.

How Barry gets out remains to be seen, but we've been given teases on the effects it has on him. According to Todd Helbing, Barry's time in the Speed Force will partly help him leave some of that angst behind himself.

"[The Speed Force] let him deal with all of the baggage [from the past three seasons]. When he comes out, he's sort of left that all behind."

Given Barry's decision in the finale, viewers should absolutely expect some tension between him and Iris. After all, he made this big decision without consulting with her, the love of his life.

While their romance will be stronger than ever, we'll, in fact, see the pair go to couples therapy! Kreisberg revealed in a recent interview that the couple will have some blocks to get through when Barry returns.

"Barry and Iris keep comically clashing inadvertently because she's used to being in charge, and he's used to being in charge, so they wind up going to couples therapy to work through it.

The two of them with the therapist is some of the funniest stuff we have ever done on this show, but it also leads to a deepening of their relationship."

It looks like the therapy is going to pay-off, which brings us to our final highlight...

That's right, ladies and gentlemen: Barry and Iris are finally getting married this season. When that will be is still a mystery, but Kreisberg has confirmed that a wedding is happening.

"They are finally going to get married this season and then it's going to be: Can they stay married with everything that's coming up against them?"

The CW-DC producers have been teasing that "romance" is a key theme in this year's 4-show crossover. Could the heroes of Berlanti's DC-Verse be coming together for the iconic couple's wedding?

Be sure to let us know what you're excited about for the fourth season in the comments below!

The Flash Season 4 premieres on Tuesday, October 10 at 8/7c on The CW.