Hamyd was charged with "association with terrorist criminals" and remanded in custody.
He was sent back to France from Bulgaria on Friday on the basis of a European arrest warrant issued in Paris.
Hamyd arrived in Bulgaria on 26 July and tried to enter Turkey two days later but was denied entry and placed in a Bulgarian detention centre.
He claimed to want to visit Turkey as a tourist but French sources said that the route he had taken - by train through Hungary and Serbia - is the one usually taken by would-be Syrian jihadis.
He had also frequently consulted jihadi and Syria-related website, a source told the AFP news agency.
Hamyd, whose sister Izzana was married to Kouachi, told his family that he was heading for Morocco but one of his sisters alerted police to his departure.
After the Charlie Hebdo attack, while he still at school, Hamyd was named as a possible accomplice of Chérif and Saïd Kouachi but his teachers confirmed that he had been in class at the time of their killing spree.
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