Maye Musk said her son has been sharing investment advice with her since he was 14 years old.

The 74-year-old model said on Sunday that over 35 years ago Elon Musk asked her to buy stock in a company he “really believed in,” despite advice from a stockbroker friend who said the investment was a “bad idea.”

Elon Musk’s mother shared the anecdote on Twitter after her son provided some stock-picking advice. The richest man in the world told his Twitter followers to buy stock in companies that make products they “believe in” and not to “panic” when the market does.

Maye Musk shared an example of the billionaire’s investment philosophy in action. The model said that in the 1980s she invested about 1,000 South African Rands, equivalent to about $1000 US dollars, into the stock her son recommended. It was the most she was willing to lose on the stock, she said.

But Elon Musk’s faith in the company quickly paid off and the investment tripled, Maye Musk said. As the stock climbed, the model said she “panicked” and sold her shares.

“You weren’t happy,” Maye Musk said on Twitter, addressing the tweet directly to her son. “That stock continued to rise. You also thought it was unfair that I split the winnings between you, @kimbal and @ToscaMusk.”

Maye Musk did not specify how quickly the stock price rose from 1,000 South African Rands to 3,000 or which company Elon Musk asked her to invest in. A spokesperson for the model declined to comment on the issue and said Maye Musk does not typically comment on family interactions.

Elon Musk’s advice came just days after he sold 9.6 million shares in Tesla, valued at $8.5 billion. The sell-off is likely to fund his $44 billion purchase of Twitter.

It was not the first time the richest man in the world shared investing advice. Earlier this year, Elon Musk said it was “generally better to own physical things like a home or stock in companies” than dollars “when inflation is high.”

Maye Musk expanded on her experiences in investing on Twitter. She said on Sunday that she bought her first stock in 1969 for 100 South African Rands and later put it under Elon Musk’s name in 1971 when he was born. The same stock helped the Tesla founder move from South Africa to Canada in 1989.

In a previous interview with Insider, Maye Musk emphasized that she helped her children grow by encouraging them to pursue their individual interests. During his childhood, the Tesla founder expressed a deep interest in books and computer programming. In April, Elon Musk said during a TED conference that his success has largely been driven by his desire to answer key questions surrounding the meaning of life.

The model and mother of three wrote about her family, as well as her first experience with the stock market in her book “A Woman Makes a Plan.”