Randy Jackson believed Adam Lambert was going to win American Idol in 2009.

The 'Trespassing' star appeared on the TV talent show five years ago and he finished runner-up to Kris Allen.

Lambert is due to return to the programme next week alongside fellow contestant Chris Daughtry to mentor this year's hopefuls.

Speaking to reporters on Thursday (February 13), former Idol judge Jackson admitted that he thought Lambert and Daughtry would win their respective series.

He said: "I wanted to have them [return to mentor]. They were actually in the trenches as people we were judging...and they can tell it from a completely different side. The two of them are so different, but they are also so equally, really, really talented. Both of their seasons, I thought both of them would win."

A trailer for the mentor episode has now been unveiled and it sees Lambert help guide some of this year's wannabe stars.