Before they were the greatest rock band of all time, the Beatles were four mop-topped teen idols -- and the reigning teen idol of today, Justin Bieber, paid tribute to their legacy with a performance of 'Let It Be' behind the scenes of a recent episode of 'The X Factor.'

Bieber was on hand to serve his stint as a co-mentor for this season's group of over-25 contestants, and the clip embedded below captures him sitting at the piano while his partner in mentoring, L.A. Reid, looks on appreciatively.

It's got nothing on the original, of course -- and it's easy to mock the squeaky-voiced pop star's chutzpah when it comes to covering a classic in front of TV cameras -- but it's worth noting that, for what seems like an off-the-cuff rendition, Bieber seems to know the song pretty well, performing 'Let It Be' without the aid of sheet music or written lyrics. And lest you think we're giving him too much credit, remember that many of the youthful contestants on this season's 'X Factor' name younger acts like the Jonas Brothers as influences; as we reported earlier this year, a fair number of kids these days don't even know who the Beatles were.

Keeping that in mind, Bieber's 'Let It Be' cover is something like a public service. Check it out below.

Watch Justin Bieber Cover the Beatles' 'Let It Be'