CECELIA Ahern, best-selling novelist, TV show writer, all-around literary entrepreneur - and, last but not least, the youngest daughter of Irish Prime Minister Bertie Ahern - is in a teary mood these days, but she's hardly sad.

Rather, she's crying tears of joy for all the success that's coming her way, particularly with the big-screen adaptation of her first novel, P.S. I Love You, which is coming to our screens on December 21 with an all-star cast that includes double Oscar winner Hilary Swank.

Cecelia, still only 26, saw the completed film for the first time a couple of months ago, she said, and, well, she cried her eyes out.

"I cried solidly for two hours, not because it's sad, but because it's so personal to me and so emotional," she told Ireland's Sunday Tribune.

"You know, there were things there that came from me and my boyfriend, from me and my family, it was based on my personal stories and when you're seeing it on the big screen for the first time, it's just like, 'Oh my God!'

Indeed. Young, gorgeous and oh-so talented, Cecelia has come a long way from the sneers she heard about being "Bertie's girl" after landing her first big book contract a few years back. There's no way she'd achieve the success she has - three more best-sellers after P.S., and scripting the American TV hit comedy Samantha Who? - purely on family connections alone.

Cecelia gathered her family and friends recently for a screening of the film, and more waterworks ensued.

"There wasn't one person I didn't want in that room and it was a really emotional time for me, " she says. "There were 30 people sniveling their way through the film."

Her dad has seen the finished product, but he didn't shed a tear.

"He actually didn't, but I could hear him laughing and he was clearly touched by the story. But there were no tears."