Simplify the following text for a Grade 7 native English-speaking person.
Original: Dong Zhuo was assassinated in 192 by his foster son LÃ 1\/4 Bu as part of a plot orchestrated by Interior Minister Wang Yun .
Simplified: After some fierce battles , LÃ 1\/4 Bu knew that his position was lost , and killed his foster father Dong in 192 .