Stewart's public mea culpa last week sent shock waves through the entertainment industry and fans of the blockbuster "Twilight" films. The final installment in the saga is due out in November.
Us Weekly first reported the affair between Stewart, 22, and Rupert Sanders, the 41-year-old director of "Snow White and the Huntsman." The magazine featured a photo of Sanders kissing Stewart on its cover last week, prompting swift, abject public apologies from both.
It may not have been enough. After the news broke, moving trucks were spotted outside the home that Stewart and Pattinson shared.
According to reports, Pattinson had bought a $5 million home in Los Angeles and was planning to propose to Stewart within weeks.
"Friends of Robert have told us that this was the woman that he wanted to spend the rest of his life with and he was actually very close to proposing when he heard about the affair," said Dina Sansing of Us Weekly magazine.
The two starred in the "Twilight" films as the lead characters. Fans have been enamored that their on-screen romance carried over into their real lives.
Responding to rumors that he and Stewart had already tied the knot, Pattinson told Blackbook magazine in an interview published July 21 - just days before news of the scandal broke: "No one ever knows what is true or what isn't … It's not. At least, not yet. But it is true that Kristen has always done something to me that others haven't."
Sanders, 41, is married to model Liberty Ross, 33. They have two children together.
Stewart and Pattinson, 26, have been together for three years. Despite the current tension reportedly between them, they are expected to appear together at MTV's Video Music Awards in September.
They're also slated to do a promotional tour in the fall for "Breaking Dawn, Part 2," the final film in the "Twilight" series.