This week, Netflix unveiled the teaser and first poster for Enola Holmes which arrives on Sept. 23.

Soon after the poster's release, however, many noticed a major historical error in the artwork.

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Starring Stranger Things' Millie Bobby Brown, Enola Holmes is a Sherlock Homles spinoff about the historic detective's younger sister. Alongside Bobby Brown, Henry Cavill, Helen Bonham Carter and Sam Claflin also star in the film.

Earlier this week, Netflix released the first teaser and poster for the upcoming film. Shortly after the release, however, many began to notice a major historical error in the poster's artwork.

Behind the actors, various historical London landmarks are present including Big Ben. Since the film takes place in the 19th century, however, some noticed an inaccuracy in the poster's artwork. The Portcullis House appears just behind Big Ben, a structure that wasn't built until 2001.

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Twitter user @gray, a designer, was one of the first to notice the historical inaccuracy in the artwork.

At this time, Netflix has not commented on the poster's error. However, the streaming service has released the official synopsis for Enola Holmes.

England, 1884 – a world on the brink of change. On the morning of her 16th birthday, Enola Holmes (Millie Bobby Brown) wakes to find that her mother (Helena Bonham Carter) has disappeared, leaving behind an odd assortment of gifts but no apparent clue as to where she’s gone or why.

After a free-spirited childhood, Enola suddenly finds herself under the care of her brothers Sherlock (Henry Cavill) and Mycroft (Sam Claflin), both set on sending her away to a finishing school for “proper” young ladies. Refusing to follow their wishes, Enola escapes to search for her mother in London. But when her journey finds her entangled in a mystery surrounding a young runaway Lord (Louis Partridge), Enola becomes a super-sleuth in her own right, outwitting her famous brother as she unravels a conspiracy that threatens to set back the course of history.

Based on the beloved book series by Nancy Springer, Enola Holmes is a dynamic new mystery-adventure that introduces the world’s greatest detective to his fiercest competition yet: his teenage sister. The game is afoot.

Enola Holmes marks Bobby Brown's first producing credit and premieres on Netflix Sept. 23. A brief teaser of the film is available to watch below.

Are you planning to watch Enola Holmes? Let us know in the comments below.