These days with smartphones at the ready to film any incidents, it's hard to keep a secret. Nonetheless, the cast and crew of The Fall should take a bow, after they managed to keep the show's main actor in the dark.

Jaime Dornan's father was drafted in for a cameo appearance in the serial killer drama. "Jamie had finished filming and had no idea I was going to be in it," explained his father, Jim Dornan, to The Belfast Telegraph. "It came as a real surprise when he found out."

Jim - who is a retired obstetrician and gynaecologist - said that the idea of appearing in the show, was conceived by the The Fall's writer and producer, Alan Cubitt. "I met Alan socially and he asked me to take part in The Fall."

The 68-year-old admitted that he only had one line, but had a little difficulty getting it just right. "I thought my scene would end up on the cutting room floor!"

After a few takes, the line, "Can the Assistant Chief Constable please provide us with an update on the progress of the Operation Music Man task-force?" was good enough to satisfy the director John Lynch.

"John Lynch was lovely - he was very helpful," Jim confessed. "He had kind words when I got it right and smiled sweetly when I got it wrong. I really enjoyed it and it was a very interesting morning. I would say it was awe-inspiring."

Series 3 of The Fall continues on RTE1 on Sunday.