The 100 season 3
Octavia and Bellamy in The 100 season 3 episode 5 promotional pictures The CW

The 100 season 3's upcoming episode will be all about Bellamy Blake's betrayal and the strained relationship between him and his sister Octavia, all thanks to Charles Pike, who has been elected the new chancellor of the Sky Crew.

The previous episode of the post-apocalyptic series saw Bellamy turning anti-Grounder and siding with Pike, in the wake of another attack by the Ice Nation at Mount Weather. Also, the fight until death between Roan and Lexa ended with a sword in the Ice Queen's heart.

Episode 5 of The 100's third season is titled Hakeldama and the promo for the episode teases a war brewing between the Sky Crew and the Grounders. The video opens with Pike declaring: "This land is ours now," as all his supporters cheers him. Looks like Pike alongside Bellamy declared a war on the army Lexa sent to protect them.

"What happened here is an act of war," Clarke tells Lexa as we see Octavia looking at bodies lying around. Marcus Kane is not happy, as he tells Bellamy: "They were here to help us." Then we see several injured Grounders as Bellamy admits to Pike: "We went too far."

Later, Abby comes to Clarke and asks: "Is there anything we can do to prevent retaliation?" The video ends with Kane telling Thelonious Jaha: "The war you predicted is about to happen."

This looks like the episode when Octavia's relationship with her brother Bellamy falls apart. In the season 3 trailer released back in January, we had seen Octavia punching her brother and telling him: "You are dead to me."

Showrunner Jason Rothenberg spoke to Hollywood Reporter about Bellamy's turn to the dark side and added that it was "based on what your perspective of the Grounders is".

Rothenberg explained: "We know the Grounders are not all bad. But Bellamy's worldview is formed by the fact that when has a Grounder ever proved they're anything but hostile? Lexa abandoned them and left him to die at Mount Weather and he lost friends because of that. They attacked him personally, mercilessly in season one. But they had their reasons for doing it. So for Bellamy, it becomes under the influence of Pike."

Although the showrunner affirms that Bellamy is a good boy and is just influenced by Pike, he said: "Pike, this season, shows up and he has a different view that's informed by a different set of circumstances that are 100 times worse than the experiences our heroes have had. Bellamy becomes influenced by Pike's view and his charisma, especially after he loses Gina. It's a dark turn but I don't think he's a bad guy."

The 100 season 3 episode 5 airs next Thursday (18 February) at 9pm EST on The CW.