I read on another forum that the filmmakers intented to have Simba tell Timon and Pumbaa that his father is dead and that it's all his fault, when they asked what he'd done, and Timon then say "Wow, you do have a dark past."
Even though Simba, in the final film, stated he didn't want to talk about his dark past, but let's say you are in the filmmakers's shoes, so which you would prefer: that Simba tells about his past or the way his past remains a secret until Nala tells them?