Robert Pattinson and Kristen Stewart's Low-Key Concert Night
08/08/2009 AT 08:25 AM EDT
The Twilight stars snuck into Bobby Long's concert at Hotel Cafe about three songs into his set with Pattinson's close pal Marcus Foster (who wrote a song on the Twilight soundtrack) on Thursday. The group watched the performance from a curtained off area on the stage where there was sound equipment and a few bar stools.
"Robert was super low-key when he walked in," an onlooker tells PEOPLE, adding Stewart, 19, and Pattinson, 23, went unnoticed by fans the entire night. After Long, a friend of Pattinson's, finished his set, the group quickly exited the venue and jumped into a waiting cab.
The two headed out for a second night in a row Friday, this time catching Foster's show at Hotel Cafe.
"Kristen and Rob, just the two of them, came in and walked towards the curtained-off area on stage where they watched Marcus," says a source. "They seemd to go unnoticed."
Stewart and Pattinson later showed up together with a group of pals at the Chateau Marmont, and hung out well into the night.
While the two have remained tight-lipped on their relationship, the actors have spent time together off set – and are more than costars, according to a source.
"Word on the set of Twilight is that [Michael] Angarano, [Kristen's boyfriend], and she are completely broken up," a source tells PEOPLE. "While people don’t want to talk about it, everyone is pretty convinced that Pattinson and Stewart are hooking up."
Reporting by BLAINE ZUCKERMAN