Rob Kardashian has "fallen hard" for Blac Chyna.

A source said: "Rob has fallen hard for Blac Chyna. She makes him super happy and this is the first time that he's felt so optimistic about life in years."

And Blac has been encouraging the 28-year-old sock designer to live a healthier lifestyle and diet and exercise to shed the pounds.

The insider added to PEOPLE magazine: "She helps keep Rob in check with his health and makes sure he is abiding by his diet and exercising.

"He feels there's strong potential for this relationship to go a long way but for now they are very content and compliment each other really well. For the first time in forever, Rob seems very excited about the future."

Meanwhile, the couple are said to be keen to "protect" each other at whatever cost.

A source said: "Rob was upset that Chyna got arrested and spoke to her in the car when he picked her up about it. She said sorry to him but was thankful he came to get her. He wants to protect her. She wants to protect him ...

"Chyna knows his family is not happy about them dating but still couldn't care less. She wants the family to see that she is a good fit for Rob and she cares about him. She is aware her getting arrested was not the best thing, but s**t happens. If they can't seem to accept her then so be it!"