Jeffrey Gundlach, chief executive officer of DoubleLine Capital, said on Monday at the Sohn Investment Conference that his best idea for investors is to buy interest rate volatility on long maturity U.S. Treasuries.

Gundlach, known as Wall Street's Bond King, said U.S. interest rates "cannot maintain the low volatility" they have experienced in the past eight years and it is "not inconceivable" that interest-rate volatility could double.

Investors can express the bet through both put and call options at the same strike, or sale, price, he said. Puts give investors the ability to buy, while calls provide the chance to sell. Landing a number where the rate rises or falls more than the total premium on the option could allow investors to book big profits.

Gundlach recommended using the iShares 20+ Year Treasury Bond ETF as a way to execute the trade. “I think this is an extremely compelling time to do this trade and an extremely important environment where outcomes are so binary,” he said.