Simon Harper says Rosie Marcel and Amanda Mealing are "devoted to each other in real life".
The \'Holby City\' and \'Casualty\' producer revealed that although the pair play rival surgeons Jac Naylor and Connie Beauchamp in their respective shows, they "really relished" the chance to act alongside each other in the recent crossover of medical dramas, which joined forces for a mash-up as the hospital in which both dramas are set is targeted by a cyber-attack.
Speaking on \'The Zoe Ball Breakfast Show\' on Radio 2, Simon said: "Rosie and Amanda really relished this opportunity. It\'s funny because they both play arch rivals on the show but are devoted to each other in real life.
"There are so many wonderful things in the episode tonight but that\'s kind of the crux of the whole thing they\'re the kind of iconic strong female surgeon characters in both show."
Amanda, 51, currently plays Connie in \'Casualty\', but previously portrayed the boss of 41-year-old Rosie\'s character Jac in \'Holby City\'.
And Simon admitted the pair\'s history adds a "delicious tension" to the show - which will continue on Tuesday evening (05.01.19).
He explained: "What\'s brilliant is the two characters have this shared history because Jac is the \'Holby\' character but Connie is the \'Casualty\' character, but Connie used to be in \'Holby\' and she used to be Jac\'s boss.
"So there was that kind of tension and rivalry going on and now they\'re equals.
"Jac won\'t let her forget it so there\'s that kind of delicious tension and shared history underscoring the scene."
Simon said it was "very tricky" working out the filming schedules for both shows.
He said: "If we\'re talking about unsung heroes I actually have to give a massive shout out to the two schedulers on both shows because scheduling it was such a huge challenge."
