Colin Farrell's evolution from lad-about-town to doting dad is officially underway. He turned up Sunday night at the London premiere of his new Irish ensemble film, "Intermission," waving a baby picture of his son, James, born in September, PEOPLE's London bureau reports.

Joining Farrell at the premiere -- held at Notting Hill's intimate Electric Cinema -- was a posse that included Jake Gyllenhaal, Alessandro Nivola and Cillian Murphy. The new papa, who has been picked as one of PEOPLE's Sexiest Men, appeared amiable and well-behaved -- "Intermission" costar Kelly MacDonald even called her leading man "charismatic."

Not that Farrell has turned his back on the nightlife. Word has it that during filming, Farrell took MacDonald and Shirley Henderson (the only two non-Dubliners in the "Intermission" cast) for a few nights on the town to welcome them to his home city.

And in response to an earlier comment by "S.W.A.T." costar Samuel L. Jackson that the day would come when Farrell would stop partying, Farrell appeared nonplussed. "Did he say that?" Farrell asked, surprised. "What a joker."

Sporting long blond locks for a role in the film "Alexander," the heartthrob also dismissed rumors of a romance with his "Alexander the Great" costar Angelina Jolie, saying instead that the two are trading parenting tips.

"Angelina and I work together. Do you go out with people you work with?" Farrell cracked.

"Intermission" first appeared in the U.S. at the 2003 Telluride Film Festival; it's due to be released stateside next spring, according to IMDB.com.