Pope Francis brought Robert Prevost to the Vatican in 2023 as the powerful head of the office that vets bishop nominations, one of the most important jobs in the Catholic Church. On Thursday, he ascended to become Pope Leo XIV — the first pontiff from the United States.

NBC News’ Savannah Sellers interviewed Pope Leo XIV’s brother, Louis Prevost, about how he felt when his sibling was elected leader of the Catholic Church. Prevost also spoke about what he’s expecting from a brotherly relationship with a pope.

Robert Prevost has been named the new pope. But why did he opt to select the title Leo XIV? Here's a closer look at its history.