Elizabeth Olsen
Cast member Elizabeth Olsen poses at the premiere of "In Secret" in Los Angeles, California February 6, 2014. The film opens in the U.S. on February 21. REUTERS/Kevork Djansezian Reuters

Elizabeth Olsen knows who her favourite Olsen twin is. The “In Secret” star has revealed her favourite sister between Mary Kate and Ashley Olsen, and the answer puts her in trouble with the unfavoured sister.

The BAFTA-nominated guest starred in the U.S. late night talk show “Watch What Happens Live” on Wednesday, when a caller asked her to pick between her older sisters.

“You have two sisters, I also have two sisters, you have to prefer one over the other,” the caller told the actress. “Who do you like better: Mary-Kate or Ashley?”

Host Andy Cohen approved the question, adding, “There has to be one that is more in your favour today that you’re vibing on.”

Instead of playing coy, Elizabeth surprisingly answered the question, albeit a bit hesitantly.

“Ashley remembered my birthday, but I don’t hold grudges against Mary-Kate forgetting mine,” Elizabeth, who has just turned 25 on Sunday, said.

Mary-Kate had an excuse, though. She was out of town when her younger sister celebrated her birthday.

“Mary-Kate’s literally going to come home from her vacation and shoot me that I said that,” Elizabeth quipped.

When Andy noted that Mary-Kate could have just sent a text message to Elizabeth from Jamaica, Elizabeth argued in defence of the former child star, “Yeah, but how often when you’re on vacation do you look at your phone and read the date?

“You don’t really read the date. You’re just like, ‘This is day three of my vacation.’”

She added that she’s very close to the twin sisters, who started their Hollywood career at the tender age of nine months old.

“I’m very close with my brother as well. I should have just said him,” Elizabeth said of their older brother, Trent. “That would have been the easier scapegoat.”

Mary-Kate and Ashley Olsen became stars when they were just babies. They made their acting debut sharing the role of Michelle Tanner on the sitcom “Full House.” Since then, they have become household names, starring together in various TV, film, and direct-to-video projects, even producing some of those themselves.

Elizabeth, meanwhile, was older when she began her acting career at age four. She co-starred in some of her older sisters’ productions, although it was her roles in the 2011 thriller “Martha Marcy May Marlene” and the horror flick “Silent House” that got her noticed in the business.

She is currently starring in the erotic thriller “In Secret,” which will be released on February 21. She will also be in the upcoming sci-fi film “Godzilla,” which is scheduled for release on May 16.