The Mystery Unveiled: Walter poisoned Brock in season 4 of Breaking Bad but the truth didn't come out until the following year. The character Brock Cantillo (Ian Posada) was the six-year-old son of Jesse Pinkman's girlfriend, Andrea (Emily Rios). Brock greatly admired Jesse and the two would often hang out and bond. After Jesse and Andrea broke up, he continued to send them money through Saul Goodman.

The pair reunited in Breaking Bad season 4, but shortly after, Brock was rushed to the hospital with a serious illness — which turned out to be because Walt poisoned Brock.

At first, Jesse believed that Brock was given the ricin that was intended for villain Gus Fring. He thought that Walt stole the ricin and gave it to Brock as a way to punish Jesse for getting too close to Gus. When confronted, however, Walt gave Jesse the idea that it must have been Gus who used the ricin to harm Brock.

Sadly, Jesse was right as Walt caused Brock's illness to get Jesse to help him kill Gus on Breaking Bad using the Lily of the Valley plant, but it isn't clear how Walt poisoned Brock with the berries.

The Sinister Act: Breaking Bad creator Vince Gilligan provided more details about Walt poisoning Brock at San Diego Comic-Con in 2013. The writers of Breaking Bad referred to the incident as Walt becoming the "Evil Juice Box Man," imagining him injecting the poison into Brock's juice box.

Off-camera, Walt had somehow planted the juice box in Brock's lunch at school, making sure only he came in contact with it. The rest of the plan involving the ricin stolen by Huell then played out on-screen. Thankfully, Brock survived and recovered. Walt later encountered Brock and seemed very uneasy around the young boy.

The Turning Point: While Walter White had many breaking points throughout the series, many fans consider Walter White poisoning Brock as the moment Heisenberg really turned evil, dropping any remnants of the morality he once had and focusing on retaining power regardless of who he had to harm to achieve it. Jesse eventually put the puzzle pieces together and figured out that Walt was responsible, causing an enormous amount of turmoil between the two men.

Jesse also confronted Saul Goodman, who admitted that he did help Walt but didn't know that his intention was to poison a young boy.

Later on, Walt admitted to Jesse that he poisoned Brock with a Lily of the Valley plant just to keep Jesse on his side for them to orchestrate the death of Gus Fring, but by that point, their relationship was already in shambles. Shortly after, as Jesse was being dragged to Jack Welker's Compound, Walter White also confessed to Jesse that he witnessed Jane Margolis die and chose not to intervene.

After Walt set Jesse free in the Breaking Bad series finale, many thought one of the first things Jesse would do was find Brock and take care of him.

The Aftermath: However, 2019's El Camino gave Jesse Pinkman barely enough time to tie up loose ends and get a shot at freedom after he was kidnapped by Jack Welker and the Neo-Nazis. Before escaping to Alaska, Jesse sent a letter to Brock, but the contents of the letter remains between the writers and Aaron Paul to this day.

Vince Gilligan originally planned to have Jesse read it as a voiceover but later chose to keep its contents a secret, which is why El Camino didn't reveal Jesse's letter.

A Question of Morality: Seeing the decent and caring person he is in the first episode of the series, fans may be left to fully realize how Walt turned into the monster he had become.

Walt had been on a gradual and shocking journey to becoming a more ruthless man. Perhaps the moment the audience truly saw what this man was capable of when it came to protecting his empire was allowing Jesse's girlfriend Jane to die in her sleep. However, at that moment, at least the audience could see the intense guilt Walt felt about the decision and its consequences.

The poisoning of Brock seemed to be the act that convinced Walt there was no line he would not cross and he became deadlier as a result.

Ordering the execution of all of Mike's men in prison was a terrifying display of his power. Walt killing Mike was also a shocking moment as it was the first murder he committed that was truly unnecessary and that he simply did out of anger.

The poisoning of Brock may have opened up the floodgates of Walt's villainous actions, but from nearly taking a young boy's life to using it to manipulate Jesse into committing another murder to using Gus's death to solidify his empire, Walt poisoning Brock remains his most heinous act on Breaking Bad.