In the Bible, to know often means an intimate knowledge and regard for someone. This doesn't just mean sexually (though that is where the phrase "known in the Biblical sense" came from, as in Genesis 4:1.) Here's a summary of this meaning of "know" in the Bible:
When the Bible speaks of God knowing particular individuals, it often means that He has special regard for them, that they are the objects of His affection and concern. For example in Amos 3:2, God, speaking to Israel says,“You only have I known of all the families of the earth; therefore I will punish you for all your iniquities.” The Lord knows about all the families of the earth, but He knew Israel in a special way.* They were His chosen people whom He had set His heart upon. See Deuteronomy 7:7,8; 10:15. Because Israel was His in a special sense He chastised them, cf. Hebrews 12:5,6.*God, speaking to Jeremiah, said, “Before I formed you in the womb, I knew you,” (Jeremiah 1:5). The meaning here is not that God knew about Jeremiah but that He had a special regard for the prophet before He formed him in his mother’s womb. Jesus also used the word “knew” in the sense of personal, intimate awareness. “On that day many will say to me, ‘Lord, Lord, did we not prophesy in your name, and cast out demons in your name, and do many mighty works in your name?’ And then will I declare to them, ‘I never knew you; depart from me, you evildoers’ “ (Matt. 7:22,23). Our Lord cannot be understood here as saying, I knew nothing about you, for it is quite evident that He knew all too much about them – their evil character and evil works; hence, His meaning must be, I never knew you intimately nor personally, I never regarded you as the objects of my favor or love. Paul uses the word in the same way in I Corinthians 8:3, “But if one loves God, one is known by him,” and also II Timothy 2:19, “the Lord knows those who are His.” The Lord knows about all men but He only knows those “who love Him, who are called according to His purpose” (Rom 8:28) – those who are His!
The same page goes on to extend that type of "knowledge" to "foreknowledge":
Although the term ‘foreknew’ is used seldom in the New Testament, it is altogether indefensible to ignore the meaning so frequently given to the word ‘know’ in the usage of Scripture; ‘foreknow’ merely adds the thought of ‘beforehand’ to the word ‘know’. Many times in Scripture ‘know’ has a pregnant meaning which goes beyond that of mere cognition. It is used in a sense practically synonymous with ‘love’, to set regard upon, to know with peculiar interest, delight, affection, and action (cf. Gen 18:19; Exod. 2:25; Psalm 1:6; 144:3; Jer. 1:5; Amos 3:2; Hosea 13:5; Matt 7:23; I Cor. 8:3; Gal. 4:9; II Tim. 2:19; I John 3:1).* There is no reason why this import of the word ‘know’ should not be applied to ‘foreknow’ in this passage, as also in 11:2 where it also occurs in the same kind of construction and where the thought of election is patently present (cf. 11:5,6). When this import is appreciated, then there is no reason for adding any qualifying notion and ‘whom He foreknew’ is seen to contain within itself the differentiating element required. It means ‘whom he set regard upon’ or ‘whom he knew from eternity with distinguishing affection and delight’ and is virtually equivalent to ‘whom he foreloved’. This interpretation, furthermore, is in agreement with the efficient and determining action which is so conspicuous in every other link of the chain – it is God who predestinates, it is God who calls, it is God who justifies, and it is He who glorifies. Foresight of faith would be out of accord with the determinative action which is predicated of God in these other instances and would constitute a weakening of the total emphasis at the point where we should least expect it….It is not the foresight of difference but the foreknowledge that makes difference to exist, not a foresight that recognizes existence but the foreknowledge that determines existence. It is a sovereign distinguishing love.”
This is a common understanding for Calvinists and Lutherans, who believe "foreknew" in Romans 8:29 (and elsewhere) to mean "foreloved," in contrast to Arminians who believe it means "foresaw."
My question is, is there support for the idea of "foreknowledge" being "forelove" anywhere in the writings of the church fathers? If so, where? If not, when is it first introduced and in which writings?