As others have mentioned that the phrase Et Tu Brute refers to betrayal, I would posit that a better phrase for surprise would be “הֲגַ֥ם שָׁא֖וּל בַּנְּבִאִֽים”. This is an ancient Yiddishe Mashal and is brought in Nevi’im.
Shmuel Alef , Kapital Yud.
“When all who knew him previously saw him speaking in ecstasy together with the prophets, the people said to one another, “What’s happened to the son of Kish? Is Shaul too among the prophets?”
But another person there spoke up and said, “And who are their fathers?” Thus the proverb arose: “Is Shaul too among the prophets?”