Rome's 5th emperor, Nero Claudius Caesar Augustus Germanicus, holds a dark place in history — and today we look back at one of his most chilling acts: the murder of his step brother, Tiberius Claudius Caesar Brittanicus.

Unlike Nero, who had been brought into the imperial family through adoption when his mother, Agrippina the Younger, married Claudius, Britannicus was Claudius' natural-born son. This made Britannicus a direct rival for the throne. What made matters worse for Nero was that Britannicus seemed to excel at everything. No matter how many humiliating situations Nero deliberately placed him in, Britannicus handled each one with grace, consistently impressing those around him and refusing to stumble.

One evening during a card game, Nero saw an opportunity to embarrass Britannicus publicly. He challenged him to stand up and sing before the entire gathering, fully expecting it to be a mortifying spectacle. But Britannicus stunned the crowd instead — not only with his remarkable vocal talent but also with the emotional weight of his song, which told the story of how Nero had always been treated as the family favorite. The audience was moved to sympathy. For Nero, that was the final straw. From that moment, he resolved to have Britannicus assassinated.

To carry out his plan, Nero turned to Locusta — the very same poisoner responsible for their father's death. The initial dose she prepared proved ineffective. But after numerous tests, trials, and errors, Locusta finally concocted a faster-working poison, which Nero wasted no time bringing into the dining room himself.

The assassination unfolded at a dinner party attended by family members and several other nobles. The method was cunning: a hot drink was first sampled by a food tester to avoid suspicion, and once it was deemed too warm to drink, cold water laced with the poison was added to cool it down. The effect on Britannicus was immediate — he was said to have "lost alike both voice and breath." Nero casually explained it away as an epileptic fit, something he claimed Britannicus had experienced since childhood. Britannicus died sometime between December and his 14th birthday on February 11th, AD 55, which was when he would have been when he would have grown into manhood. His death occurred just four months after his father's.

As for Nero, the poison didn't stop with Britannicus — he would go on to poison his mother later in his rule as well.