- “I'm not going anywhere without my brother.”
- — Octavia to Indra.
Because of the one child law on the Ark, Bellamy and Octavia are the only known siblings among the Sky People. They are half-siblings.
Ever since Bellamy sided with Pike in Season Three, their relationship has been strained. After Lincoln's death, Octavia disowned Bellamy, blaming him for Lincoln's death. However, events have made Octavia overcome her own personal demons and restores her relationship with Bellamy.
Aurora Blake, Bellamy and Octavia's mother, was forced to keep her second pregnancy a secret because of the one child law on the Ark. A seven-year-old Bellamy watched his mother give birth to his sister and even helped keep her quiet after the birth. After the child was born, Aurora told Bellamy to name her. He had learned about the Roman emperor, Augustus, and named his sister after the emperor's sister, Octavia. Aurora told Bellamy that Octavia was his responsibility. He told her he loves her very much and promises to keep her safe, no matter what may happen.
Because Octavia was an illegal second child, she had to be kept hidden in their room, never venturing out. Bellamy would tell her stories and play with her, telling her about the Ark. Their mother would also read them mythology, which Octavia loved. Octavia would also help Aurora, who was a seamstress on the Ark. In order to find out about the surprise inspections ahead of time, Aurora was sleeping with an Ark Guard and she was also trying to get Bellamy a position on the guard. During these inspections, Octavia was forced to hide under the floorboards and wait quietly until they were done. Bellamy told her to tell herself, "I am not afraid."
Octavia was finally exposed a year before they were sent to earth. Bellamy had become an Ark Guard Cadet and was able to get duty during the Unity Day masquerade party. He sneaks Octavia out of their room so she could attend and promises her that he'll keep her safe and deliver her home before their mother even knows they're gone. The party is disrupted by a solar flare alert, requiring everyone to show ID. Since Octavia didn't have any ID, they knew they would be caught. Bellamy tells her to go straight back to their room and hide but Octavia admits to him that she doesn't know how to get back. Commander Shumway notices that Bellamy has his shock baton out and starts to question them. Bellamy begs Commander Shumway to let her go, but he refuses stating Bellamy is not a guardsman yet. Octavia tries to run but is easily captured. Bellamy suddenly loses his sister, his mother, and his chance to be an Ark guard and becomes a janitor.
A year later, Bellamy is approached by Commander Shumway who tells Bellamy that 100 prisoners are being sent to the ground, his sister among them. He offers Bellamy the chance to go to Earth and protect Octavia but only if he shoots and kills the Chancellor. Bellamy accepts the deal and stows away on the dropship.
- Bellamy and Octavia Blake are siblings on the CW television show, The 100.
- Bellamy named Octavia. He had learned about the Roman emperor, Augustus, and named his sister after the emperor's sister, Octavia.
- Aurora, their mother, told Bellamy that Octavia was his responsibility.