The 24-year-old singer - who won the ninth season of the Fox talent contest last year - performed his Brand New single 'Beautiful Like You' on the show, which also saw 21-year-old New Yorker Karen Rodriguez eliminated from the series.
He said: "I'm really happy with the single. It's one of my favourite songs off the album and we put a lot of time into it."
Giving advice to this year's hopefuls, Lee added to 'American Idol' host Ryan Seacrest: "It's great to be back. Just remember why you tried out in the first place. You guys are fine, no matter what happens."
However, Lee - who beat runner-up Crystal Bowersox to be crowned winner of the show in 2010 - admitted he still finds it "weird" watching this year's hopefuls battle it out on 'American Idol'.
Speaking on KIIS-FM's 'On Air With Ryan Seacrest' yesterday (17.03.11), he explained: "It's weird watching the show after being through that; I know what they're going through and I can see it sometimes. I'm like, 'Oh boy'. "