I came across this sentence:
The book I am using, explains に is used here to indicate the passive form. I looked up a video explaining it by Misa from Japanese Ammo. She explains that one of the reasons to use passive form, is to express feeling upset, angry or embarrassed. Apparently Verb te-form + しまいました can be used to express regret or embarrassment. Now, Misa does not explain in that lesson that the passive could also be formed with Verb te-form + しまいました, the website that explains Verb te-form + しまいました does not include passive examples. Can you build the passive with Verb te-form + しまいました instead of the passive form of the verb?