Kim Kardashian's "work ethic" has been key to her success, according to her personal trainer

He said: "People don't realise that they're super hard workers and if you put that work ethic towards anything and you're going to have success."

Gunnar also revealed that Kim and her sister Khloe are hard workers in the gym, too.

He explained that the reality stars really commit themselves to their workout routines.

He told Us Weekly: "It's not about the workout itself, it's about the intensity. They both go for it and they give everything to their workouts. That's why the family is successful."

Kim previously claimed that she doesn't care what people think of her.

The brunette beauty hit back at her critics, arguing that her talent lies in "marketing and the business behind selling products".

Asked about her talents and the keys to her success, Kim explained: "I'm like, 'Well, we have a TV show.' But just because we're not singing and dancing and acting on the show doesn't mean that the fame didn't come from that.

"But then, I would write that as a hashtag, not bad for a girl with no talent, because people used to be like, 'Well, what do you do? What's your talent?' And I'm like, 'Didn't know I needed one.'

"I mean, I can give you a million f****** talents. I can cook well, use my toes for anything. I could tell you the weirdest f****** s*** on the planet. But I think my talent is marketing and the business behind selling products and knowing what the customer wants and making it feel attainable, but also a bit unattainable at the same time.

"I wouldn't say that's a talent. I think it's a bit of magic and business savvy. Maybe it is talent, I don't know."