Efron, 23, and Hudgens, 22, have been going out since they were teenagers.
"It's nothing dramatic," one insider told E! Monday. "There's no third party involved."
"They were together for so long. It just ran its course," another source said.
The celebrity couple and parents of two young children have been together for four years.
Rev. Run, a founding member of the rap group Run-DMC, married Richie and Madden Saturday at a winter-themed ceremony attended by about 150 people, including reality TV star Khloe Kardashian and disc jockey Samantha Ronson.
"Joel and Nicole have looked up to Rev. Run, so they wanted him to officiate," one guest told UsMagazine.com. "They both appreciate his family values and he is an inspiration for both. They both also respect his faith, too."
Elizabeth Hurley: British model and actress Elizabeth Hurley confirmed via Twitter she has separated from her husband, Indian businessman Arun Nayar.
Hurley and Nayar started dating in 2003 and married in 2007.
"Not a great day. For the record, my husband Arun and I separated a few months ago. Our close family & friends were aware of this," Hurley messaged on Twitter Sunday.
People.com said Hurley's message came as a response to a story in Britain's News of the World reporting she is romantically involved with cricket player Shane Warne.
Josh Duhamel: Josh Duhamel, Katie Holmes and Blair Underwood have been tapped to announce the nominations for Hollywood's upcoming Golden Globes ceremony.
They are to join Hollywood Foreign Press Association President Philip Berk in revealing the names of nominees Tuesday at The Beverly Hilton Hotel in Los Angeles.
The 68th annual Golden Globe Awards are to be handed out Jan. 16. The show is to air on NBC from the Beverly Hilton Hotel with Ricky Gervais serving as host.
The Globes will recognize the best in film and television for 2010.