The elegant little chapel is a Gothic building and the only remnant of the 15th-century fortified manor house of Troménec.
Inside are a sarcophagus and a tombstone. The tombstone is that of François de Kermavan or Carman, who was killed in a duel in 1600 and is shown in a roughly carved recumbent position. The tombstone is that of his killer, Guillaume Simon de Troménec, who practiced increased banditry in the region.
According to legend, he raided the estate of the Bishop of Léon, who called his protector, the young François de Kermarvan, for help. This was sure of his fencing skills and challenged the experienced Sieur de Troménec to a duel, but was killed. He then continued his assaults more than ever. The bishop then excommunicated him and made the Seigneur de Troménec an outlaw who could be punished with the wheel. Out of remorse or prudence, he submitted, paid a heavy fine and, most importantly, undertook to build a chapel of expiation in his own castle, where François de Carman was buried.