Mufasa's backstory is explained in the new Lion King prequel, and it manages to make him completely different from Simba in the original story.

Based on previous Disney releases, Mufasa will likely be streaming on Disney+ in March or April, but the time frame may be shortened by the film's box office performance

The Lion King outperformed Paramount’s Sonic the Hedgehog 3 at the international box office, solidifying its global dominance. While both films competed strongly during the holiday season, Mufasa leveraged its international appeal to pull ahead of Sonic 3 in worldwide earnings.