13 things you need to know about the 'third twin' Elizabeth Olsen

But what do we know about the mysterious third Olsen? Elizabeth is only two years younger than the twins but she’s spent most of her life out of the spotlight.

Recently though, the 26-year-old has emerged as a very credible actress, and she plays Scarlet Witch in the Avengers sequel Age of Ultron.

Here’s what you need to know about the girl of the moment.

1. She’s not the only other Olsen, the girls have a brother called Trent. Their dad also remarried and had two other kids, so she has a half brother and sister Jake and Courtney too.

2. Elizabeth (nicknamed Lizzie) made a cameo appearance in an Olsen twins movie when she was four.

3. At the age of 17 she moved to New York to study theatre at the Tisch School of the Arts and has said she felt theatre seemed “safer” than film.

4. No one really knew who she was until she popped up at Sundance 2011 where she was seen playing an escaped cult member in indie drama Marth Marcy May Marlene, which was critically acclaimed. People called her the festival’s breakthrough star that year.

5. At 23 she starred in Josh Radnor’s new romantic film Liberal Arts, but so far she hadn’t really broken into the mainstream.

6. A few years later she started working with Aaron Taylor-Johnson on three films – Captain America: The Winter Soldier, Godzilla and the Avengers sequel.

7. According to E!, she almost reconsidered a career in acting back in 2004 when rumours circulated about Mary-Kate battling anorexia, saying that the media was “abusive to my sisters and I didn’t really want to be in that industry”.

8. Her favourite actress was always Michelle Pfeiffer, who apparently inspired her from an early age. She told Marie Claire: “I never had a heart-throb or a band I loved, but I had Michelle Pfeiffer. She was the reason I wanted to be an actor.”

9. She has a wicked dress sense.

10. She’s said that the most romantic present she ever received was a bag of Cheetos from a boyfriend she had at 15.

11. Elizabeth got engaged to Boyd Holbrook, an American model and actor, in March 2014 but they split in January this year.

12. Elizabeth is fiercely private and doesn’t even have any social media accounts, which is pretty unheard of from a celeb trying to build up their profile these days.

13. Speaking about her sisters, she told the Guardian: “Their fame made me more determined to study. I knew I wanted to be an actor, but I also didn’t want to start working when I was under 18.

“I decided that as long as I felt confident and worked hard for it, instead of having it handed to me, no one could take that away from me…. I never got any job because of my sisters. I could have pulled a few strings through them, but I never needed to.”