“The rally in bonds is a once in a millennium event, but it’s absolutely mathematically impossible for bonds to get any kind of returns like this going forward whereas stock returns can repeat themselves, and are likely to outperform,” Jeremy Siegel, finance professor at the University of Pennsylvania’s Wharton School, said. “If you missed the rally in bonds, well, then that’s it.”

With Treasury yields hovering around record lows and values high, yields will have to eventually go up. Additionally, as the economy recovers and investors take on riskier assets, the move away from Treasuries will also fuel the rise in interest rates.

Investors seeking to bet against the fall in Treasuries and rise in interest rates may take a look at inverse Treasury ETFs such as ProShares UltraShort 20+ Year Treasury (NYSEArca: TBT), ProShares Short 20+ Year Treasury (NYSEArca: TBF) or Direxion Daily 30-Year Treasury Bear 3x Shares (NYSEArca: TMV). [Risk-On Rally Sends Treasury ETFs Into Tailspin]

iShares Barclays 20+ Year Treasury Bond

For more information on U.S. Treasuries, visit our Treasury bonds category.

Max Chen contributed to this article.