The terms for Mubadala's 2010 investment "could simply be a way of giving them a little kicker for what both parties knew was an overvalued equity infusion three years earlier," said Pieniazek.
Shares of Blackstone, which is based in New York, have lost half of their value since they were first sold in the 2007 initial offering at $31 each.
Following Carlyle's offering, Mubadala will be restricted from selling parts of its stake for 12 to 24 months, according to Carlyle's registration statement. The Abu Dhabi company, the second-largest Carlyle owner after the founders, is also restricted from holding a stake bigger than 19.9 percent.