"Today was the best day of my life," Young, 32, tells PEOPLE. "Diana and I are in it forever. She's my best friend."
DeGarmo, 25, wore a form-fitting Sareh Nouri gown with pearls and rhinestones.
"It was the first dress she tried on," says Renée Strauss, the LA-based luxury bridal expert who organized the wedding. "She knew immediately that it was the perfect dress for her."
The wedding colors were purple and yellow. Young wore a custom-made box suit with a crest designed by Strauss: the couple's monogram with "Forever Young" emblazoned underneath.
"They wanted to put their personal touch on the wedding," says Strauss, who has also coordinated weddings for Heather Locklear and Valerie Bertinelli. "We all worked together to make sure every detail was special."
The ceremony began with six flower girls – all nieces of DeGarmo and Young – walking down the aisle with baskets of flower petals. Each basket had a different word on it, spelling out a message to the groom: "Hey Ace. Here Comes Your Bride."
A harpist played the Wedding March as DeGarmo walked down the aisle. The wedding was officiated by music writer Fred Bronson. After the couple exchanged vows that they wrote themselves, they walked back up the aisle to the strains of Led Zeppelin's "All of My Love."
The 250 guests included fellow Idol finalists Elliot Yamin, Michael Johns and Kevin Covais. Several of DeGarmo's costars from The Young and the Restless also attended, including Christian LeBlanc and Tracey Bregman.
After the ceremony, the guests headed to the reception. On the menu: filet mignon, chicken, salmon or pumpkin ravioli. There were two wedding cakes: a traditional vanilla, and a banana chocolate chip. The couple recorded an original song entitled "I Do" for their first dance.
"This was the best way to start the chapter of my life as Mrs. Young," DeGarmo tells PEOPLE. "I'm over the moon with joy and happiness about our wonderful wedding. I can't wait to spend my life with my husband!"
Brian Leahy Photography
For more on the couple's nuptials, including exclusive photos of the ceremony and reception, pick up the upcoming issue of PEOPLE.