Simplify the following text for a Grade 4 native English-speaking person.
Original: Later in 241 , the crown prince Sun Deng died â '' an event that left open the issue of succession and appeared to mark the start of a precipitous decline in Sun Quan 's mental health . In 242 , he appointed his son Sun He , born to Consort Wang , crown prince .
Simplified: After his son Crown Prince Sun Deng died in 241 , he made his now-oldest son Sun He Crown Prince .