Nina Dobrev spent the night in the emergency room.

Nina Dobrev

Nina Dobrev

The 'Vampire Diaries' star was forced to spend a night in hospital over the weekend for an unknown reason, but was supported through her stay by her best friend Julianne Hough, who took to Instagram to document the event.

Julianne, 31, posted a video of their trip to the ER on her Instagram story, and said: "Well, this is my night at the emergency room on a Sunday night with guess who?"

And text on the clip read: "Who would I be at the Emergency Room with on a Sunday night?! Thank god I went to visit this little sheesh! (sic)"

A few hours later, Julianne revealed her mystery friend was in fact 30-year-old Nina, although she didn't disclose the reason the actress had found herself in hospital.

However, a source confirmed to E! News that the star is "fine".

Last year, Nina and the professional dancer opened up on their lengthy friendship, which they both feel has lasted for decades.

Nina said: "It feels like we met when we were 2 years old because I feel like I have known you my entire life. We are goofy, we like to laugh, we like to play with our dogs and hang out and watch movies and get ready together and go places together.

"We just like to be around each other. I can only speak for myself, but Julianne is such a positive, awesome person. She has an infectious energy that you just want to be around, so selfishly I am just trying to get a little bit of her energy transferred to me

Whilst Julianne added: "We're like yin and yang - like same thing with Nina - you also have an infectious energy. You're always the person that's inclusive of everybody and always making sure everybody is having fun, and we're like a spontaneous combustion of energy when we're together, at least we think so."