The older sister of the model-and-actor has praised the couple's strong relationship, admitting she has no problem with the 'Wrecking Ball' singer's wild antics because she makes him ''happy''.
She said: ''I think they're adorable. I mean if my brother's happy then I'm happy and so that's all that matters to me.''
The couple - who have been dating for almost a year - were thought to be receiving pressure from Patrick's family to split up, with rumours suggesting they believed she was a bad influence, but Katherine has now revealed she is just pleased he has found someone to love.
She continued: ''You just want your siblings to be happy so if they're with someone that makes them happy in a happy and healthy relationship then I'm happy.''
The 25-year-old journalist - who is the daughter of actor Arnold Schwarzenegger and journalist Maria Shriver - also opened up about life at home by revealing her mother is strict when it comes to her kids using mobile phones during family dinners.
Speaking to Mario Lopez on 'Extra', she explained: ''She makes us all put our phones in the centre of the table so no one is on their phone. It's such a good rule because you do see people, especially couples on dates, and they're all on. It's so sad.''
From Halsey to Foo Fighters, these tracks tell a parent’s story with raw honesty.