[1] In The Voyage of the Dawn Treader he sets sail for the Lone Islands and beyond to look for the seven lords who had been sent to explore the lands beyond the Eastern Ocean.
And finally he persuaded the seven noble lords, who alone among all the Telmarines did not fear the sea, to sail away and look for new lands beyond the Eastern Ocean, and, as he intended, they never came back."
A bracelet bearing Octesian's family crest was found on Dragon Island, where the Dawn Treader stopped for repairs after being caught in a storm.
In the film version, Edmund, Caspian and Eustace find his skeletal remains wrapped around various gold and jewellery implying that he was either killed by another dragon who was already there or had been starved to death after being tempted to stay on the island for its treasures despite the harsh conditions.
Caspian later identified the solid gold body as Restimar's when Coriakin informed them that he had been the only one missing from the party when the remaining four lords arrived on Duffer Island.
He is a broken man by the time he is rescued, so when the voyage sets anchor at Ramandu's Island the crew leave Rhoop behind to enjoy a blissful, enchanted "sleep without dreams".
Their hair has grown exceptionally long when Caspian and his followers find them; and they are in a deep sleep from which the travellers are unable to wake them.
Caspian and his friends are told that the only way to awaken the three sleeping lords is to sail voluntarily to the end of the world or as close as possible, and to leave behind at least one member of the crew.
After the Dawn Treader has sailed east for some time in this quest, Aslan appears to Caspian, and informs him that Reepicheep, Edmund, Lucy, and Eustace are to continue on towards the end of the world, but that the other crew members are to go back.