While the establishment of the official liturgical celebration of Christ the King only occurred for the first time in the 20th century, St. Francis de Sales referred to our Savior this way a number of times in his writings.
His quotes below may help you prepare for this Feast!
To receive the grace of God into our hearts they must be emptied of our own vain-glory. Humility repels Satan, and preserves the graces and gifts of the Holy Spirit within us. All the saints, but particularly the King of Saints and His Mother, have always honored and cherished this blessed virtue more than any among the moral virtues.
IDL 3: 4
Yes, the King of glory does not recompense his servants according to the functions they perform but according to the measure of the love and humility with which they exercise them.
IDL 3: 2
How ardently I long for the Savior’s heart to be king of all our hearts.!
LST 129
Spiritual lovers, spouses of the heavenly King, do indeed from time to time contemplate themselves in order to see if they are adorned so as to please their Beloved. This is done by examinations of conscience, by which they cleanse, purify, and beautify themselves as well as they can, not in order to be perfect, not to satisfy themselves, not from a desire to make progress in virtue, but out of obedience to the Bridegroom—out of the reverence they have for Him, and the desire they have to please Him.
SPC 228
in the early councils they set up a throne in the midst of all the assembled bishops and placed on it the book of the holy Gospels to represent the person of the Savior, king, teacher, director, spirit, and unique heart both of councils and of the entire Church.. So greatly did they honor the signification of God’s will as expressed in that divine book! God’s love is seated within the Savior’s heart as on a royal throne. He beholds through the cleft of his pierced side all the hearts of the children of men. His heart is king of hearts, and he keeps his eyes fixed on our hearts. Just as those who peer through a lattice see clearly while they themselves are only half seen, so too the divine love within that heart, or rather that heart of divine love, always clearly sees our hearts and looks on them with his eyes of love, while we do not see him, but only half see him.
TLG 1, 5:11, 263