EastEnders viewers noticed not one but two familiar faces in Albert Square.
Fans of the show watched on Tuesday as Maria Connor and Tracy Barlow rowed furiously over the pollution problem in Weatherfield.
Maria raged as she feared for her son, Liam, who suffers with asthma.
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She was mocked by Tracy, and the whole thing was caught on camera by a journalist, the Mirror reports.
The footage seemed to have made its way to Walford, and was watched by Tiffany Butcher.
As Tiffany sat in Whitney's living room, she showed her the video on her phone as she said: "Have you see what this mum from Weatherfield is doing for her little boy with asthma?
"This turns into such a barney!"
In the Emmerdale episode which aired earlier, Liam and Amelia had joined forces to create a social media page for his allotment.
Coronation Street's Gary Windass later showed their viral video to girlfriend Maria.
Gary said: "I was online and there's a doctor in a village in Yorkshire and he's been growing veg for the community.
"He thinks it helps his mental health. I wouldn't mind trying some of those dance moves."
Maria raised her eyebrows as she said: "I'm not sure you could keep up, Gary."
The soap crossover sees huge dramas such as Corrie, EastEnders and Emmerdale join forces to highlight the impact of climate change.
Fans are loving it, with many taking to Twitter.
One wrote: "CORRIE CROSSOVER!! Love it!!"
Another said: "Soap crossover week is bizarre! Corrie’s Maria Connor in EastEnders!"
A third said it "destroyed the internal reality of the EastEnders universe" and they have previously "mentioned Coronation Street as a fictional programme".
EastEnders airs Mondays, Tuesdays, Thursdays and Fridays on BBC One
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