Kelly Clarkson sees John Legend as her biggest ''threat'' on 'The Voice'.

The 36-year-old pop star has admitted that John, 40, is a serious competitor on the upcoming season of the NBC show, which sees Kelly, John, Adam Levine and Blake Shelton compete as coaches.

Kelly confessed: ''I've never been more terrified to be on this show with a coach than John Legend.

''He's everyone's threat, they don't know it yet. He's the threat.''

Adam, 39 - who recently performed during the Super Bowl halftime show with Maroon 5 - is also aware of John's threat on the show.

Adam hailed the award-winning star, admitting he's ''incredibly talented and very charming''.

He told People: ''John is a threat. I mean, John has like 4,000 awards and he's incredibly talented and very charming.''

Meanwhile, Kelly previously admitted she's turned into ''a vampire'' since becoming a mother.

The 'Because of You' hitmaker - who has a four-year-old daughter called River and a two-year-old son called Remington - revealed that since having her own kids, she's realised she is ''not a morning person''.

Kelly - who has been married to Brandon Blackstock since 2013 - said: ''I'm not a morning person. I love the night. I am a vampire.''

The pop star also revealed that when she does have time to herself, she loves to take part in quilting - which is the process of sewing two or more layers of fabric together to make a thicker padded material.

Asked about her favourite hobby, Kelly shared: ''I love putting on vinyl and having wine and quilting. It's fun. I'm not great at it, but I like it.''