After being kidnapped by extremists a month earlier in the city of Sirte, a video was then released allegedly showing the men being executed.
After their deaths, the men were officially considered as martyrs by the Coptic Orthodox Church of which they belonged.
Their killings received widespread media attention. Speaking to Premier about the outpouring of love for the men, Bishop Angaelos of the Coptic Orthodox Church in the UK said: "It influenced a lot of people around the world because this was a stepping up a level of brutality that we probably hadn't seen.
"There was also a marked triumphalism about it. These people were being flaunted in a way that really dehumanised them."
While their deaths hit the headlines, the forgiveness offered by the men's families drew widespread respect. Bishop Angaelos said: "Their own families were so gracious and forgiving - it really sent out a message that the power in that scenario was not of the men holding knives, it was of those who met their deaths with such honour and dignity and faith.
The Church of England's General Synod stopped in silence to remember the men at their start of its meeting at Church House in Westminster.
Listen to Premier's Marcus Jones speaking with Bishop Angaelos.