Passive Voice: It wasn’t known by me that anyone else was here.
Explanation: In the active voice, the subject performs the action (I didn’t know), while in the passive voice, the subject receives the action (It wasn’t known by me). To change the active sentence “I didn’t know anyone else was here” to passive voice, we make “anyone else was here” the new subject, and “I” becomes the agent, introduced by the preposition “by”. The verb “didn’t know” changes to its passive form “wasn’t known”.