Steve Madden, the shoe designer who has worked with Mary-Kate and Ashley Olsen for five years on their two very profitable shoe lines, claiming the experience is "painful, painful."

But Madden isn't going anywhere.

"They’re very demanding, they’re very tough," he told Fashionista "You know, just tough, tough. They want what they want. And so we worked hard to get that done. They are difficult. They are exacting," Madden added.  "They are a pain in the ass. But they’re very good though."

It has to be noted that Steve Madden is one of the pioneers of the designer shoe businessand at 54 is more than twice the age of the Olsens.  On the other hand, he admitted that their business relationship works because: "They’re very grown up, very worldly. And I’m very immature. So we meet in the middle."

It has to be mentioned that Mary-Kate, 25, is now dating Olivier Sarkozy, the 42-year-old half-brother of former French President Nicolas Sarkozy.

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