"She doesn't want to be known as Rob's girlfriend," the source says of the 22-year-old daughter of Sean Penn, 53, and Robin Wright, 47. "She's afraid to get serious with him and lose her privacy."
Not that the Twilight star, 27, is putting any pressure on the 5-foot-7 stunner to settle down. After his rocky three-year relationship with Kristen Stewart, 23, imploded in May, "Rob isn't ready to be exclusive with anyone right now," an insider says. "He's just enjoying himself."
For more details on Pattinson's relationship with Penn, watch this week's Hot Stuff video, as explained by Us Weekly Entertainment Director Ian Drew and special guest, "Here to Kill the Pain" singer Jason Charles Miller.
Also in the roundup: Halle Berry's daughter Nahla prayed for a baby sister; Casey Kasem's kids fight to see him; and much more!