St. Theodore of Canterbury says Filioque (A.D. 680)

The most remarkable instance of the continuance of the formula, ‘of the Son’, at this period is our great Archbishop Theodore, himself a native of Tarsus, well versed, as is shown in his Penitential, in the usages of the Greek church, with which he parallels or contrasts those of the West. He shows himself also familiar with the Greek fathers, and the East of his own day had such confidence in him, that the 6th General Council waited for him. On Sept. 17 A.D. 680 , not quite two months before the opening of the 6th General Council, Nov. 7, A.D. 680, he presided over the Council of Hatfield, in which the Confession of faith was drawn up, which embodied the Filioque:

In it, it is declared:

‘We have expounded the right and orthodox faith, as our Lord Jesus Christ, Incarnate, delivered to His Apostles who saw Him in bodily presence, and heard His discourses, and delivered the Creed of the holy fathers: and in general all the sacred and universal synods and the whole choir of the Catholic approved doctors of the church [have delivered it]‘

And then after a brief confession of faith in the Holy Trinity in Unity, and of the Lateran Council of A.D. 649, it thus concludes : —

‘And we glorify our Lord Jesus Christ as they glorified Him, adding nothing, taking away nothing: and we anathematize in heart and word whom they anathematized: we receive whom they received: glorifying God the Father without beginning, and His Only-begotten Son, Begotten of the Father before all ages: and the Holy Ghost, proceeding from the Father and the Son, ineffably; as those holy Apostles, and prophets, and doctors, whom we above commemorated, have preached‘

On the Filioque: In Regard to the Eastern Church, Edward Bouverie Pusey – Page 125-26

Picture from – http://www.oodegr.com/english/biographies/arxaioi/Theodore_Canterbury.htm