Priscilla Chan with Beast Zuckerberg
Allyson Magda Photography
05/28/2012 at 02:00 PM EDT
The guests at Mark Zuckerberg's surprise backyard wedding
first saw bride Priscilla Chan
, 28-year-old Zuckerberg's longtime girlfriend, turning the corner in a beautiful white gown
, accompanied by the couple's dog, Beast.
The 1-year-old Puli, an Internet celebrity in his own right (his Facebook page
has 570,000 likes), wore his shaggy Hungarian sheepdog hair pinned up over his eyes. Chan, 27, walked him on a ribbon-like white leash down the makeshift aisle.
Beast first joined Chan and Zuckerberg in their Palo Alto, Calif., home in March of last year, two months after he was born. He has since pooped on Zuckerberg's rug, visited the Facebook offices and met the Dog Whisperer
, Cesar Millan.
Most of all, he has become an important and meaningful part of his owners' lives, as evidenced by the prominence he gets on their respective Facebook pages. Both Zuckerberg and Chan
, known as Dad and Mom on Beast's page, feature their beloved dog in their cover photos online.
For Beast, the biggest honor of all might have been walking Mom down the aisle so she could marry Dad.
For more on the billion-dollar couple's nuptials and to see exclusive photos, pick up the latest issue of PEOPLE, on newsstands now.