Inside the notoriously private life of Mary-Kate and Ashley Olsen's older brother, Trent.

From when they were toddlers, Mary-Kate and Ashley Olsen have been the most recognisable twins in the world.

And with their sister Elizabeth Olsen gaining international fame in 2011 after her successful breakout role in the thriller Martha Marcy May Marlene, together they are three of the most famous siblings in Hollywood.

But you may not know that there is a fourth person who completes the Olsen siblings: James Olsen. Who actually goes by his middle name, Trent.

In 2014, Mary-Kate and Ashley Olsen launched their ‘Elizabeth and James collection’, a fashion line named after their two siblings.

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The Olsen siblings. Image: Social.

Unlike his sisters, the older brother of the Olsen sisters didn't pursue a career in acting, although he is now involved in producing Hollywood films.

In fact, Trent nearly become a childhood actor himself, according to a University friend of the Olsen brother who spoke to the New York Post in 2014.

When he was six-years-old he reportedly auditioned for a role in Tales From the Crypt and was successful in being offered the job. "But his parents wouldn’t let him take it," the friend recalled.

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The Olsen siblings and their mum honouring Ashley and Mary-Kate with a star on the Hollywood Walk of Fame on April 29, 2004 in Hollywood. Image: Getty.

He went on to live a normal life at school, out of the public eye, with one friend telling the publication: "He would sell his sisters’ autographed photos. I definitely bought one. We all did!"

Growing up with his famous twin sisters, the Olsen brother, now 34, only ever made a few rare appearances with his sisters, including when they were being honoured with a star on the Hollywood Walk of Fame in 2004.

Trent went on to graduate from college after attending the University of Southern California where he was described by friends as a "jokester".

His friend told the New York Post: "He has like 3,000 Facebook friends, and Trent thought it was funny to change his birthday every three months or so. He'd receive 100 posts on Facebook wishing him a 'Happy Birthday' four times a year".

He now works at Storm King Productions, in the feature film and television division. And although he has some of the best connections in the industry, he's determined to create his own success.

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His friends describe him as a "jokester". Image: Instagram.

"They’re incredibly close," the friend told the publication. "But I think he wants to do it all basically on his own."

And it seems acting talent is inherent in the family, with the friend adding: "I hope he will take up acting again. He's freakin' amazing. Lizzy [Elizabeth] was hidden for many years, and now she's tearing it up. And I know he'll do the same thing."