A brand new Bel-Air megamansion has sold for $75 million—one of the largest deals ever closed in Los Angeles, according to people with knowledge of the deal. The buyer hails from China, those people said.

Earlier this month, a Holmby Hills estate formerly owned by television producer Aaron Spelling sold for about $120 million, setting a record for the priciest home ever sold in the Los Angeles area.

The...