The Playboy entrepreneur dated the twins between 2008 and 2010, but asked them to leave the Playboy mansion when his relationship with Crystal Harris became more serious.
He was also said to be unhappy that both Kristina and Karissa had found new boyfriends, but invited them back to the mansion in June 2011.
"I'm hearing good things about the twins on Big Brother UK. Makes me proud," Hefner wrote on Twitter.
The twins entered the Celebrity Big Brother house on Thursday alongside X Factor's Frankie Cocozza and TOWIE star Kirk Norcross.
Cocozza has already admitted that he would like to get the former Playboy bunnies into the hot tub.