Patriarch Bartholomew and Pope Benedict in Istanbul in 2006 (Source)
From the Orthodox Christian Network:
His All-Holiness closely cooperated with the Pope during the tenure of Pope Benedict, issuing joint statements on contemporary problems facing humanity and realizing official exchange visits, but above all resuming in 2007 the conversations of the Joint International Commission for Theological Dialogue between the Orthodox and Roman Catholic Churches (established in 1980 and interrupted in 2000).
Statement by His All-Holiness Ecumenical Patriarch Bartholomew At the Announcement of the Retirement of Benedict XVI, Pope of Rome (February 11, 2013)
It is with regret that we have learned of the decision by His Holiness Pope Benedict to retire from his Throne, because with his wisdom and experience he could have provided much more to the Church and the world.
Pope Benedict leaves an indelible mark on the life and history of the Roman Catholic Church, sealed not only by his brief papacy, but also by his broad and longstanding contribution as a theologian and hierarch of his Church, as well as his universally acknowledged prestige.
His writings will long speak of his deep theological understanding, through his knowledge of the Fathers of the undivided Church, his familiarity with contemporary reality, and his keen interest in the problems of humankind.
We Orthodox will always honor him as a friend of our Church and a faithful servant of the sacred proposition for the union of all. Moreover, we shall rejoice upon learning of his sound health and the productivity of his theological work.
Personally, we remember with emotion his visit to the See of the Ecumenical Patriarchate over six years ago, together with the numerous encounters and excellent cooperation, which we enjoyed throughout the duration of his primatial ministry.
From the Phanar, we pray that the Lord will manifest his worthy successor as the head of the sister Church of Rome, and that we may also continue with this successor on our common journey toward the unity of all unto the glory of God.