Momager knows best!

Kris Jenner was the driving force behind Kylie's breakup with Tyga, biographer Ian Halperin reveals in his new tell-all Kardashian Dynasty. So what was the straw that broke the camel's back? Blac Chyna's pregnancy!

"The second Chyna rolled into bed with Rob it marked the end of Tyga's Kardashian journey. Kris is one of the sharpest people one could ever meet. She's nobody's fool. And she knew there was not room for both Tyga and Chyna in the Kardashian fold. She chose Chyna," a source revealed.

Not only that, but the Kardashian clan began to realize what a loser the rapper is and decided they didn't want his name associated with their brand.

"The Kardashians had to choose one over the other. It was easy. The family hated the fact that Tyga had financial problems. There were constant rumors of bankruptcy and Tyga was evicted from several homes for not paying the rent. It was the perfect time for them to get rid of him and to focus on Chyna and Rob. The icing on the cake was when Chyna announced she was pregnant. Days later Tyga was out like a bad dog," the source added. Ouch!

Now their main concern is making sure the "Rack City" crooner keeps his mouth shut and doesn't spill any Kardashian family secrets!

"A year ago they were worried about Scott dishing everything because nobody knows more about them then Scott, he's been in their lives since the beginning of their tv show and knows everything. Now they are most worried about Tyga talking. With Scott they were able to sit him down, offer him a boatload of money to stay on the show and keep under their control. Tyga seems to be going his own way. He's holding the cards. Until Kris is able to sign him to remain in their stable the Kardashians will have sleepless nights worrying that Tyga will dish all their secrets to the media," the insider explained.

Considering he's basically bankrupt and career-less, we bet Kris can throw some money at the problem and get him to go away for good!