<P> Aaron is one of the rescued Oceanic Six , and the general public are told he is Kate 's son , while Claire is listed as among the passengers who did not survive the plane crash . At Christian Shephard 's memorial service , Carole Littleton , who has recovered from her coma , tells Jack she and Christian had a relationship which produced Claire , revealing her to be Jack 's half - sister . Eventually , before departing to return to the island , Kate reveals to Carole that Aaron is Claire 's son . Kate tells Carole that she is going back to try to find Claire , and leaves Aaron with his grandmother . </P>
when do we find out claire is jack 's sister
At Christian Shephard 's memorial service