Robertson appeared on CNBC with Kelly Evans and unequivocally called the stock market a bubble. Not only that, he said it was the Federal Reserve's fault.

Robertson said he thinks low interested rates have inflated stock market valuations. There simply isn't anyplace else for money to flow.

Well, we're very, very high — have very high valuations in most stocks. The market, as a whole, is quite high on a historic basis. And I think that's due to the fact that interest rates are so low that there's no real competition for the money other than art and real estate. And so I think that's why the valuations are so high. I think when rates do start to go up and the bonds become more attractive to investors, it will affect the margins."

He went on to pin the blame for the overvalued markets on central bankers – not just at the Fed, but around the world.

It's the Federal Reserve's fault, and the Federal Reserves all over the world. I mean, in Germany, in order to buy a bond, until recently, you actually had to pay interest. And, you know, that's certainly going to discourage a lot of people from doing so. You know, you could get a fairly good dividend in Nestle, but if you wanted to buy a Nestle bond, you had to pay a fairly heavy penalty."

Evans said that, "Doesn't seem to make a lot of sense." Robertson agreed.

Empirical data backs up Robertson's assertion.  As Yahoo Finance reported last year, analysis shows that 93% of the entire stock market move since 2008 was caused by Federal Reserve policy.

Robertson doesn't go all the way down this road, but his comments reveal the difficult spot the Federal Reserve finds itself in. Yellen has put herself between a rock and a hard place. If she tightens, she risks bursting the bubbles. If she doesn't, she risks inflating bubbles further, leading to an even bigger crash when they finally burst. No matter what the central bankers do, they are on the road to trouble.