In January of 2008, Mary-Kate made headlines when her close friend, actor Heath Ledger, died of a prescription drug overdose.
Olsen remains silent on the matter, but sources say Ledger's staff contacted Mary-Kate through a speed-dial function on Ledger's cell phone.
Mary-Kate checked herself into rehabilitation for anorexia in 2004.
The production company owned by the twins is called Dualstar.
In 2007, they announced another line of more contemporary clothing, Elizabeth and James, which is named after their sister and brother.
They are also known for their more affordable lines Style Mint and Olsenboye.
Despite reports that police were interested in questioning her about the death of Heath Ledger, a New York Police Department spokesperson confirmed to MTV News on Friday (January 25) that officials have no plans to speak to actress Mary-Kate Olsen about the circumstances surrounding the actor's demise.
People magazine reported on Friday that funeral services for Ledger would remain private and that he would be buried in his hometown of Perth, Australia, though no official plans have been announced by his family.
Actress Mary-Kate Olsen was born on June 13, 1986, in Sherman Oaks, California.
The daughter of mortgage banker David Olsen and manager Jarnie Olsen, Mary-Kate and her twin sister, Ashley, have become among the most popular—and bankable—female personalities in America.
Released through a division of the Penguin Young Readers Group, the work features figures such as Christian Louboutin, Lauren Hutton and Bob Colacello.
It became an instant best seller, and the twins launched a promotional tour for the book.