Demi Lovato was grossed out by a snotty fan.

The 'Heart Attack' singer narrowly escaped being submerged in snot when a hysterical fan tried to shake her hand after accidentally smearing her own mucus all over it.

She shuddered: ''This girl was at a signing [in London] and she was crying so much that her nose literally dripped with snot down to her chin, and she wiped it with her hand and then went to shake mine.

''I know she probably wasn't thinking straight because she was obviously very emotional, but it was just really gross.''

The 20-year-old star also discussed her brand new duet, 'Really Don't Care', with past 'X Factor' UK contestant Cher Lloyd, who is enjoying a successful career across the Atlantic.

She explained: ''My mum and my little sister are huge Cher Lloyd fans; they were like, 'That would be awesome. That's a good idea'. Then it just kind of happened.

''I just basically wrote this song and I was like, 'Do you know what? This song would sound great with Cher Lloyd on it', so she was already in the back of my mind. I wanted to do something with another female who has a lot of attitude and a lot of sass.''

Demi doesn't understand why the British public perceives Cher as a ''brat'' and says the young starlet was very humble and unassuming in real life.

She added in an interview with heat magazine: ''What's ironic is that the first time I met her was when she performed on the 'X Factor' in the US. She was super-sweet, nothing like I expected. She's not super-sassy in person, she's actually a real sweetheart. She was awesome.''