The Historical Background

It may seem insignificant at first, but the little latin word "filioque" ("and the Son") caused a serious controversy between the Western churches and the Eastern churches. In fact, while the bigger issue was that the Eastern churches did not want to submit to the authority of the Pope in Rome, this word is one of the causes of the major division that later occurred in 1054 A.D.

The first version of the Nicene Creed adopted in 325 said simply, "We believe in one God, the Father almighty, ...and in one Lord Jesus Christ, the Son of God, ...and in the Holy Spirit."

The version of the First Council of Constantinople in 381 added some phrases: "We believe in the Holy Spirit, the Lord, the giver of life, who proceeds from the Father."

Then the word "filioque" ("and the Son") apparently began to be accepted widely by the Western churches as an addition to the creed, after the Third Synod of Toledo in Spain in 589: "We believe in the Holy Spirit, the Lord, the giver of life, who proceeds from the Father and the Son." However, this was not accepted by the Eastern churches.

[See: a) http://www.theopedia.com/filioque-clause
b) https://carm.org/what-is-the-filioque-clause-controversy-biblical
c) Wayne Grudem, Systematic Theology, Grand Rapids: Zondervan, 1994. p. 246]

Question: When did the word "filioque" ("and the Son") apparently begin to be accepted widely by the Western churches as an addition to the original Nicene Creed?