The pair are starring in new horror film In Fear and were at the film festival to promote it.
Allen's last leading lady was Jessica Brown Findlay, who played tragic Lady Sybil who died following childbirth in the last series.
No doubt little comparison can be made between the period drama and the horror film but Downton fans will be happy to see the Killiney, Co Dublin, native smiling again.
Downton is being broadcast across America -- and viewers have yet to see that scene involving Lady Sybil. Allen is the latest Downton star to make the Stateside. Dan Stevens, who played Matthew Crawley, has appeared on Broadway throughout last year and will have more time of concentrate on developing his US career following the death of his Downton character.
Jessica Brown Findlay is currently working on a A Winter's Tale with our own Colin Farrell and Michelle Dockery, who plays Lady Mary, has also been tipped for a bright future in the US.
Also at this year's film festival was Nicole Kidman, who was promoting her new flick Stoker, Mad Men star Elizabeth Moss, Dermot Mulrooney, Alexander Skarsgard, Keri Russell, Judith Godreche and Tamsin Egerton.
Also gracing the red carpet was pregnant actress Kristen Bell.