Likutei Moharan 150:1/ליקוטי מוהר"ן ק״נ:א׳

1He saw D’mut D’yukno (the countenance) of his father. (Sotah 36b)

2This is something which is very mysterious: How is it that a person’s countenance appears yet he himself is unaware of it? For certainly Yaakov did not know. Moreover, the value of the test, even though [Yosef] saw the countenance, is something which is mysterious and hidden from man.