ABC News' Erin Brady reports:

For an actress known for her eccentric dress and androgynous look - Tilda Swinton is warm and charming in person.  At 5'11 she arrived promptly on time in four inch heels sporting a buzzed haircut.  She was wearing emerald green silk pants and a shirt of the same fabric, a look she refers to as "pajamas."   

The native of Scotland is best known in the United States for her Oscar-winning portrayal of a power-craved corporate lawyer in the 2007 film "Michael Clayton," starring opposite George Clooney.  In her latest film, "We Need To Talk About Kevin,"  she tackles another complex woman:  a mother whose son goes on a murderous killing spree.

"We all know that [post-partum] happens to countless, hundreds of thousands of these women and yet nobody seems to really talk about it," Swinton told "Nightline" anchor Cynthia McFadden. "The other more covered taboo in the story that's uncovered by the film is that we don't know what we're doing as parents, on a day to day basis, we don't know what we're doing."

While Swinton was not nominated for an Oscar this time around, her portrayal has been hailed by film critics as one of her finest works. Ironically though, this Academy award winner said she does not consider herself a "real" actor, but rather sees herself as an "amateur. "

"The thing is I never intended to be an actor and I still don't picture myself with that goal," Swinton said. "It's not something I learned to do. It's not something I aim to do. It's sort of a mistake in a way."

As for her personal life, the actress dismissed published reports that she is living with two men,  her current flame and her children's biological father.  She called her actual living situation, "boring."

"There are some myths," she said. "The reality is so much more boring, fun and good, but so much more boring. People like to believe all sorts of magical ideas."

Swinton, 51, lives in the Scottish Highlands with her 14-year-old twins and her boyfriend, painter Sandro Kopp, who is nearly 20 years her junior. The twins' father, playwright John Byrne, is 20 years her senior and while Swinton said they separated seven years ago, Byrne comes to stay with them from time to time.

"John comes to us, usually," she said. "He has a studio near where we live and he lives in Edinburgh. But [the children] sometimes go to him. We all sometimes go to him."

Watch "Nightline" anchor Cynthia McFadden's full interview with Tilda Swinton tonight at 11:35 p.m. ET