Why Katy Perry & Russell Brand's Split Shocked Friends

By Marisa Laudadio

UPDATED 01/04/2012 at 02:45 PM EST • Originally published 01/04/2012 at 12:30 PM EST

When Russell Brand announced on Dec. 30 that he was divorcing Katy Perry, it wasn't just their fans that were caught off guard.

"I was shocked when I found out," a source who knows the couple tells PEOPLE. "I was really surprised that Russell filed for divorce so quickly – especially at Christmas time."

Continues the source: "I thought they would be together for a long time. Maybe not forever – but definitely not just 14 months."

"They were always laughing," the source says. "They were very affectionate, always holding hands. They seemed like they were really in love."

RELATED: Katy & Russell's Most Romantic Moments

Another source who spent time with Brand, 36, and Perry, 27, tells PEOPLE that both of them "took marriage very seriously."

"These aren't people who give up," the second source says. "I always thought they would work on their marriage if they had trouble."

• With reporting by K.C. BAKER

For more on the conflicts in Perry and Brand's marriage, pick up the new issue of PEOPLE, on newsstands Friday