Kimberly Wyatt is "not sure" she believes in marriage.

The 29-year-old former Pussycat Dolls star has been with boyfriend Kevin Schmidt for three years but doesn't know whether she wants to make their union official as the thought of doing so makes her feel very anxious.

She said: "I'm still not sure if I truly believe in marriage. We've talked about promise rings, but my anxiety levels went so crazy I had to step outside for some fresh air."

The blonde beauty also admitted she was "scared" when she started dating Kevin because he is so much younger than her.

Asked if she had ever had a Christmas kiss she shouldn't have had, she told LOOK magazine: "Yes, three years ago when my boyfriend Kevin and I started dating - I was scared because he's six years younger than me."

Kimberly has previously credited Kevin inspires her to live a more organic lifestyle.

She said: "I love how honest and pure and passionate and compassionate he is. He makes a conscious effort to live a natural and organic lifestyle and all of that has been instilled In Me. I am very inspired."

Kimberly and Kevin are often kept apart due to their hectic lifestyles but she is confident they can make their relationship work.

She has said: "He's an unbelievable guy. It takes two special people to have a long-distance relationship with my schedule but if anybody can do it, I think it's us."