"Sometimes, you don't see that the best thing that's ever happened to you is right under your nose," Lily Collins says in the latest 'Love, Rosie' trailer.

In this fourth and full teaser for the film, Lily Collins deals with the consequences of a reckless night, risking her friendship with best friend Sam Claflin and losing her chance at college in Boston in the process.

The clip sheds more light at the depth of Alex and Rosie's relationship-as friends and as best mates who are keeping their real feelings a secret from each other.

Partners in crime since childhood, the two friends face young adulthood still as mischievous as their younger selves but they must deal with a new set of feelings that neither is willing to address. Their antics grow from sharing answers in class to getting wasted and accidentally kissing each other while drunk. Fast forward to a couple of years-not to mention huge bumps along the way-Rosie finally realizes what she really feels for Alex but is already too late. She already has a daughter and Alex is already engaged.

"Life isn't always what you're expecting," clearly echoes the sentiment in this 'Love, Rosie' trailer. The question is how will Rosie face these unexpected changes in her life?

Will these complications, both internal and external, break their friendship or make their bond even stronger? And will they eventually, finally get together or not?

The trailer doesn't seem like a simple friends-become-lovers story. It also shows a girl's growth from an immature girl to a woman forced to face heavy responsibilities early in life.

Based on Cecelia Ahern's best-selling book, 'Where Rainbows End,' the 'Love, Rosie' trailer features some of this generation's roster of famous young actors such as Lilly Collins and Sam Claflin. Suki Waterhouse, Art Parkinson, Tamsin Egerton, Jaime Winstone, and Jake Manley also star in the film adaptation.

'Love, Rosie' is set to hit theatres on October 12.

Watch the full 'Love, Rosie' trailer below.