Who killed Caesar but was also his best friend?

Julius Caesar was assassinated by a group of conspirators, and one of the key figures in this plot was Marcus Junius Brutus. Despite being one of Caesar's closest friends and allies, Brutus ultimately joined the conspiracy out of a belief that Caesar's power threatened the Roman Republic. His betrayal is famously encapsulated in Caesar's last Words, "Et tu, Brute?" indicating his shock at Brutus's involvement.