Colin Firth found himself in ''agony'' on the set of 'Mamma Mia! Here We Go Again' after putting his jockstrap on the wrong way round.

The 57-year-old actor stars alongside the likes of Meryl Streep, Pierce Brosnan and Stellan Skarsgard in the much-anticipated new musical comedy, and Pierce - who appeared in the original film in 2008 - has lifted the lid on some of the on-set dramas.

He shared: ''I realised ten years had passed since the first movie, and I was going to have a reunion with a group of friends on Vis, this beautiful island in Croatia.

''I didn't take singing lessons, I didn't take dancing lessons, I just rolled up ready to enjoy it. Part of the fun of the movie is that we're this bunch of people, some of whom can do all that and some who can't.

''You can't take yourself too seriously. Especially when you have to put on Spandex for those 70s dance routines and you realise your belly isn't as flat as it was, and then you look at a photograph of yourself in the costume and you think: 'Oh Lord, what have I done?'''

Pierce admitted that he and some of his co-stars struggled to cope with some of the demands of the movie.

He recalled one particularly memorable incident involving Colin and his jockstrap.

He told the Mail on Sunday newspaper: ''Stellan, Colin and I were the old blokes, laughing about getting vertigo from platform boots, trousers that were too tight and being in agony because Colin had got his jockstrap on the wrong way round.

''On day one we had to do a huge number for 'Dancing Queen', which for me was less about dancing and more about skipping.''