Tournament and trial
On 19 January 1343, the Truce of Malestroit was signed between England and France. Under the perceived safe conditions of this truce, Olivier and fifteen other Breton lords were invited to a tournament on French soil, where he was subsequently arrested and taken to Paris.
Olivier IV's wife Jeanne tried in vain to have him set free. She seems to have tried to bribe a King's sergeant.
On 2 August 1343, Olivier IV was tried by his peers and executed by beheading at Les Halles.
In the year of our Grace one thousand three hundred and forty-three, on Saturday, the second day of August, Olivier, Lord of Clisson, knight, prisoner in the Chatelet of Paris for several treasons and other crimes perpetrated by him against the king and the crown of France, and for alliances that he made with the king of England, enemy of the king and kingdom of France, as the said Olivier ... has confessed, was by judgement of the king given at Orleans drawn from the Chatelet of Paris to Les Halles ... and there on a scaffold had his head cut off. And then from there his corpse was drawn to the gibbet of Paris and there hanged on the highest level; and his head was sent to Nantes in Brittany to be put on a lance over the Sauvetout gate as a warning to others.
This execution shocked the nobility as the evidence of guilt was not publicly demonstrated, and the process of desecrating/exposing a body was reserved mainly for low-class criminals. This execution was judged harshly by Froissart and his contemporaries.
On 26 August 1343, for her attempted bribery of the Kings sergeant, Jeanne was subsequently sentenced to banishment and confiscation of her property. She managed to evade arrest, as she was protected by Olivier's eldest son Jean, Guilaume Berard, her squire and valet, Guionnet de Fay and Guillaume Denart.
The property of Olivier IV was confiscated and then doled out to vassals of the French King.:
The chamberlain of the King, Thibault, Lord of Mateflon received property in the bailiff of Caen, the manor of Tuit, the forest of Cinglais and the iron mines of Beaumont worth about 100 Livres a year.
A relative of Charles de Blois, Jean de Derval received lands and belongings of Goulaine and L’Epine, south of Nantes, worth about 500 livres a year.
The Bishop of Leon, Pierre Benoit land owned in the parish of Guerande, worth about 25 livres a year.
