During an appearance on Watch What Happens Live Feb. 19, Elizabeth Olsen picked sister Ashley Olsen as her favorite because Mary-Kate Olsen recently forgot her birthday. Credit: Charles Sykes/Bravo/NBCU Photo Bank via Getty Images

Put on the spot! During an appearance on Watch What Happens Live on Wednesday, Feb. 19, Elizabeth Olsen was asked by a caller to pick her favorite sister: Mary-Kate or Ashley Olsen? Surprisingly, Elizabeth gave an honest answer about the world famous twin actresses-turned-designers, 27.

"You have two sisters, I also have two sisters, you have to prefer one over the other," the caller told Elizabeth on the Bravo late night talk show. "Who do you like better: Mary-Kate or Ashley?"

"Now this is a good question," host Andy Cohen said. "There has to be one that is more in your favor today that you're more vibing on."

"Ashley remembered my birthday, but I don't hold grudges against Mary-Kate forgetting mine," Elizabeth replied, hesitantly, about the twins. "She was out of town! I should have just said my brother!" the In Secret actress, who celebrated her 25th on Sunday, Feb. 16, added with a laugh.

"Ashley's in the lead today, but tomorrow MK could do something amazing," Cohen said.

"We're all very close!" Elizabeth added. "I'm very close with my brother [actor Trent, 29] as well. I should have just said him. That would have been the easier scapegoat."

"You are though, to clarify, feeling closer to Ashley today," Cohen said, teasing his guest.

"Mary-Kate is literally going to come home from her vacation and shoot me that I said that," Elizabeth joked of her sister, who is currently on vacation in Jamaica.

"I think, from the last time I was in Jamaica, text signals do work," Cohen quipped of Mary-Kate's birthday slight.

"Yeah, but how often when you're on vacation do you look at your phone and read the date?" Elizabeth argued in defense of her sister. "You don't really read the date. You're just like, 'This is day three of my vacation.'"