Ian Somerhalder fell in love with Nikki Reed as soon as they started dating.

Ian Somerhalder and Nikki Reed

Ian Somerhalder and Nikki Reed

The 'Vampire Diaries' star, who married the 26-year-old actress in a romantic ceremony at the Tuscali Mountain Inn in Topanga, California late last month, reportedly instantly knew he wanted to marry her.

A source close to the 36-year-old actor told PEOPLE magazine: "Ian is just head over heels for Nikki. He loved her from the start and constantly talks about her. They are truly in love.

"They are over the moon to finally be married."

The brunette beauty, who split from ex-husband Paul McDonald last year, previously revealed that her relationship with Ian is based on them sharing similar interests.

She said: "What's nurtured this long friendship that we've had is that we're passionate about similar things."

Meanwhile, Ian's 'Vampire Diaries' co-star Kat Graham recently confessed she believes the couple are true "soul mates".

She said: "I haven't met two people that were more of soul mates than those guys. They are so absolutely amazing. Everyone loves them, and I really can't imagine him with anyone else."

Before his marriage to Nikki, Ian had a two-year romance with his 'Vampire Diaries' co-star Nina Dobrev.