'Sherlock' Season 4 Spoiler, Air Date: Search For 'Young Sherlock' With Benedict Cumberbatch's Curly Hair Underway

Casting for a young Sherlock is underway as "Sherlock" Season 4 proceeds with its filming. The production is apparently looking for a little boy with Benedict Cumberbatch's curly hair, who will be joining the set on Monday, June 27.

In a casting call on Facebook, Nino Firetto Casting cites that the young actor must be at least 3'6" and 3'9" tall with dark curly hair and blue eyes. The part is for a 6-year-old Sherlock, which will figure in non-speaking flashback scenes that will be part of "Sherlock" Season 4 Episode 3. Filming of the episode is estimated to take five weeks.

Young Sherlock Hints 'Sherlock' Season 4 Will Be About Family?

Fan theories as to what "Sherlock" Season 4 is about have been spreading online, but producers Steven Moffat and Mark Gatiss have remained secretive about the plot, as always. In March, Moffat hinted that "Sherlock" Season 4 will be about consequences. "Chickens come to roost," he said via Entertainment Weekly.

One of the most popular speculations about "Sherlock" Season 4 is the appearance of third brother, Sherrinford, who will bring more tension between Sherlock and Mycroft. This could be the reason for the flashbacks to young Sherlock as the family's dynamics will be further expounded in the coming season. The third brother was supposed to have been hinted in the "Sherlock" episode "The Last Vow."

"Sherlock' Season 4 Introduces A Sister?

However, the iconic character of Sherlock is believed to also have a sister who was briefly mentioned in the books written by Sir Arthur Conan Doyle, per The Norwood Builder. Fans speculate that the sister has already appeared during the filming of "Sherlock" Season 4 in the past week as the Lady in Red.

The appearance of a dog on the Sherlock set also hints that "Sherlock" Season 4 could delve on the character's childhood. In the book series, Sherlock had a pet dog named Redbeard, which had been euthanized. The name also cropped up in early "Sherlock" episodes, per Digital Spy.

"Sherlock" Season 4 is set to premiere in 2017 and will have three episodes like the rest of the seasons. Aside from Benedict Cumberbatch, the show also stars Martin Freeman, Mark Gatiss and Amanda Abbington.