[Alex Murphy]

The Nicene Fathers explained this nearly 1700 years ago, Claud (I'm not showing off; the Greek is important to an understanding of what happened)....
The specific answer to what the Theotokos "added" is this, but only also from the Holy Spirit....

It's all Greek to me. How about a translation?

[Kolokotronis]

And in one Lord, Jesus Christ,
“the only begotten Son of God,
begotten from the Father before all ages,
light from light,
true God from true God,
begotten not made,
of one essence with the Father,
through Whom all things came into existence,
Who on account of us men and on account of our salvation came down from the heavens,
and was enfleshed from the Holy Spirit and the Virgin Mary
and became man”