It'll be the first time that the two popular BBC One medical soaps have teamed up in almost 15 years.
For the first time since 2005, the cast of Holby City and Casualty will join forces for what will be a two-part crossover special to air BBC One.
The first part will air on Casualty on Saturday, March 2 and the second will take place on Tueday, March 5 during Holby City.
Characters from both series will interact as their storylines are intertwined across the two dramatic, action-packed episodes.
Teasing the drama to come, the BBC said: "A major cyber-attack plunges Holby into blackout and disables most of the hospital’s automated monitoring equipment.
"At the same time Sacha (Bob Barrett) is in a car crash which injures his daughter Bekka (Francesca Barrett) and Ric’s (Hugh Quarshie) granddaughter Darla (Naomi Katiyo), one of whom might be pregnant.
"Fighting a different battle among the chaos, Connie (Amanda Mealing) is left to save the life of a member of her own team with surgery.
"As Sasha’s injuries become apparent Jac (Rosie Marcel) comes to his rescue and is ready to operate but with only one theatre available in the blackout, Connie and Jac have to make the impossible decision - which of their friends to try to save first."
Simon Harper, Executive Producer of Holby City and Casualty, announced: “We’ve known for some time there’s been major audience appetite for a mega crossover between these sister shows, so that’s exactly what we are serving up!
"You’ll see both the Casualty and Holby teams striving heroically against the odds in two episodes of pure, nail-biting, taut, emotional medical drama.
"I’m quite literally in awe of Michelle Lipton’s writing achievement and Steve Brett’s direction in pulling off this double, and so proud of both the Cardiff Casualty and Elstree Holby crews and casts in making the mind-boggling logistics work, quite aside from their creative wizardry.
"There’s so much to relish in the cross-show character interactions: an especially poignant thematic resonance between two regulars, Connie and Jac, in delicious conflict, and perhaps most vitally, who from Casualty has been secretly carrying on with whom from Holby!”