Warren Buffett is synonymous with ambition, success, and fortune. The former Berkshire Hathaway CEO was once the world’s richest man, famously dethroning Bill Gates in 2008 with a $62 billion net worth, and held the spot for quite some time.

But one of the people closest to him didn’t even know how wealthy and successful Buffett was: his own son, Peter Buffett.

Peter, now 67, didn’t realize his own father’s status until he was in his 20s. The realization happened when Peter saw his dad’s name on the Forbes list of the richest Americans, according to a 2013 Forbes interview with both Peter and Warren Buffett.

“I’m not kidding. It was when I was in my 20s that my mom and I talked at some point, because there he was, on this list,” Peter said. “And we laughed about it, because we said, ‘Well, isn’t it funny? You know, we know who we are, but everybody’s treating us differently now.’”

Peter is the youngest of Warren Buffett’s three children with his first wife, Susan Alice Buffett. Peter is an American musician, composer, author, and philanthropist who has won a regional Emmy Award, become a New York Times best-selling author, and served as co-chair of the NoVo Foundation. But Peter recalled that conversation with his mom, with little effect on his outlook or perception of his family.

“It was a fascinating switch, although not a huge one because we didn’t live in that world or a cultural framework where there was a lot of wealth being shown,” Peter said. “Our friends were as surprised as I was.”

Warren Buffett backed up his son, saying that by the time his children found out just how rich they were, they had already formed their own personalities and paths.

“The kids were formed by that time, and they knew who their friends were, and their friends were their friends because they liked ’em, and not because they were the rich kid on the block or anything of the sort,” Warren Buffett said.

Warren Buffett’s net worth and outlook on money

While Warren Buffett may no longer be the world’s richest man, he is still very much a billionaire, worth about $145 billion, making him the 10th wealthiest person in the world.

Still, Buffett has never been much of one to brag about money—and it’s not how he defines success.

“Greatness does not come about through accumulating great amounts of money, great amounts of publicity or great power in government,” Buffett wrote in his final Berkshire Hathaway shareholder letter published in November.

The 95-year-old “Oracle of Ohama,” known as one of the most successful investors of all time, also lives a very frugal life. He eats McDonald’s, drives a beat-up old car, and still lives in his modest Nebraska home, which he bought for just $31,500 in 1958. His license plate once read “THRIFTY.” Rather, he says he prioritizes helping others using his fortune, which he will ultimately pass down to his children, who will use it for their respective philanthropic organizations.

“When you help someone in any of thousands of ways, you help the world,” Buffett wrote. “Kindness is costless but also priceless. Whether you are religious or not, it’s hard to beat The Golden Rule as a guide to behavior…Keep in mind that the cleaning lady is as much a human being as the Chairman.”