我们以为他是一个英雄，原来是一个叛徒。

We had thought that he was a hero, but he turned out to be a traitor.

Source: Tatoeba

Sentence Composition

1 我们 wǒmen we; us; ourselves; our
2 以为 yǐwéi to think; to believe (often with the implication that the belief is mistaken – unless referring to one's own current belief)
3 他 tā
  1. (third-person singular) (since the early 20th century, usu. male) he; him; his
  2. (bound form) other; another; some other (as in 他日 tārì and 他人 tārén)
=4 是 shì
  1. to be (followed by substantives only)
  2. correct; right; true
  3. (respectful acknowledgement of a command) very well
  4. (adverb for emphatic assertion)
=4 是 shì variant of 是 shì
=5 一个 yīge
  1. a; an; one
  2. the whole (afternoon, summer vacation etc)
=5 一个 yīgè
  1. Combination of the numeral 一 (“one”) and the generic classifier 個／个: a; an; one
  2. same
6 英雄 yīngxióng hero

classifier: 個
7 原来 yuánlái
  1. original; former
  2. originally; formerly; at first
  3. so, actually, as it turns out
=8 是 shì
  1. to be (followed by substantives only)
  2. correct; right; true
  3. (respectful acknowledgement of a command) very well
  4. (adverb for emphatic assertion)
=8 是 shì variant of 是 shì
=9 一个 yīge
  1. a; an; one
  2. the whole (afternoon, summer vacation etc)
=9 一个 yīgè
  1. Combination of the numeral 一 (“one”) and the generic classifier 個／个: a; an; one
  2. same
10 叛徒 pàntú
  1. traitor
  2. turncoat
  3. rebel
  4. renegade
  5. insurgent