Watch: Jack Schlossberg Supports Sister Tatiana Schlossberg After Terminal Cancer DiagnosisJack Schlossberg is letting old prose express his family's unfathomable grief. Nearly a week after his sister Tatiana Schlossberg died Dec. 30 following a battle with myeloid leukemia, Caroline Kennedy's youngest child shared a collection of poetry and speeches, including one from his grandfather John F. Kennedy, pertaining to grief, loss and honoring those who came before us.