Pope Leo XIV, the first U.S.-born pontiff, was considered a longshot by many to become leader of the Catholic Church.
But John Prevost told "CBS Mornings" that he suspected it was a possibility for his younger brother.
"When Pope Francis died, someone was on the radio and was asked the question, 'who's in running for the job?' and she said there were two main candidates who were in the running, one being a cardinal from Africa and one being a cardinal from Chicago who spent most of his career in Peru and then is a cardinal in Rome. No names were mentioned, but who else could that be?" said Prevost, one of Leo's two brothers.
Prevost said he found out the life-changing news at the same time as everyone else – while watching TV. He saw his brother step onto the balcony of St. Peter's Basilica and said initially he didn't believe it, despite previously considering it a possibility.
"I just thought, maybe I'm dreaming, and then it's a moment of extreme pride, and then eventually, reality sets in, and you think, there goes the rest of his life," Prevost said. "Now he's got awesome, awesome responsibility that he has to deal with."
Since that moment, Prevost said the phone hasn't stopped ringing and there have been nonstop knocks at his door.
He had the chance to briefly speak with the new pontiff on the phone for less than a minute to congratulate him.
"He knew there were reporters in the house. He's not ready for that yet," the retired Catholic school principal said.
Chicago-born, Pope Leo XIV, formerly known as Cardinal Robert Prevost, also has citizenship in Peru. His faith has been a lifelong passion.
"He did know right away that he was going to be a priest and I really don't think in his mind there was any other option."
Considered a centrist in the church, Prevost hopes his brother's diverse background can help to unite the world's 1.4 billion Catholics.
"I am aware that my mother's parents were from Haiti and we are aware that her sisters were all born in New Orleans, but my mom was born up here in Chicago," he said. "Part of his job is to bring the Catholic community together again. It's already started."
Pope Leo XIV: The First American Pope More More Kelsie Hoffman