Actress Lily Collins believes the most important thing in any relationship is honesty.

The 25-year-old doesn't think there's an ultimate secret to falling in love and staying in love, but believes that being truthful with your partner builds the best foundation for long-term happiness, reports bangshowbiz.com.

"It doesn't matter how long it takes to get there, to be in love, as long as in the end people are honest. When you're honest it pays off,` she said.

"Everyone has their own speed at which they're honest, so I would say it's beautiful but it depends on person to person,` added Collins.

The actress plays Rosie Dunne, the romantic interest of Sam Clafin's alter ego Alex Stewart in her latest role in `Love, Rosie`, which sees the two best friends slowly realise that they have fallen for each other.