A man referred to only as “Farid K” was accused of knowing the attack was going to happen – but not the time or place.
The 30-year-old hosted his cousin Abdel Malik Petitjean in his flat in Nancy, eastern France, prosecutors claim.
He appeared before a judge in Paris where he was charged yesterday.
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Petitjean, along with Adel Kermiche, 19, murdered elderly Father Jacques Hamel in his church in Saint-Etienne-du-Rouvray in Normandy.
The gruesome pair shouted “Allahu Akbar” – God is great – before being shot dead by police last Tuesday.
Normandy mosque in mourning: Muslims pays tribute to slain priest
Petitjean’s stepfather also claimed the two lived together at times.
Farid is one of many suspects arrested after the atrocity who is still being held.
Writing in the Journal du Dimanche newspaper, French prime minister Manuel Valls said: "This intolerable rejection of Islam and Muslims… must be combatted - and it is - with the greatest strength."
And in an attack with chilling similarities, a pastor was stabbed by an asylum seeker in his home in Belgium after he refused to give him money yesterday.