Young popped the question to Diana DeGarmo on stage during last night's grand finale of the show.
Young has now told People that he first asked to set up the surprise last week.
"I called [producer] Nigel [Lythgoe] directly last week and said, 'I want to do this, I'm going to do this, is there any way I could do it at the show?'" he explained.
"He said: 'Yes, I'm not going to tell anybody until the day of... [and] I want you to figure it out with Ryan [Seacrest]."
Young added that DeGarmo's engagement ring is inspired by her love for sunflowers, while his new fiancée admitted that she was "completely caught off guard".
"I actually almost got up to go to the bathroom to fix my hair," she said. "And then I just started shaking!"
Jessica Sanchez and Phillip Phillips battled it out in the American Idol grand finale, which crowned one of them the winner.
Photo gallery - American Idol grand finale (contains spoilers):
Copyright: Fox Michael Becker