After splitting the dramas between them - one cost far more to make than the other - as well as hosting a joint launch and even producing a joint press release, the world might have hoped for a peaceful ending to such a historic collaboration. Unfortunately not.
The first instalment of Karaoke starts at 9.30pm on BBC1 on Sunday and will be repeated on Channel 4 the next night. But far from supporting its erstwhile rival, Channel 4 has scheduled the seminal Francis Ford Coppola movie, Apocalypse Now, directly against it.
This contrasts with its somewhat less punchy repeat Channel 4 put out at 9pm last Sunday - a documentary about the British bombings of Kurdistan villages in the 1920s and 1930s.
The Sunday before, Channel 4 also scheduled a documentary. That was about the exploitation of deep sleep therapy in an Australian hospital in the 1960s and 1970s.
The schedules reveal that Channel 4 has brought forward its Sunday night film by an hour in an apparent attempt to reduce the audience BBC1 attracts to the first showing of Karaoke. By contrast, the BBC plans to show Panorama in its normal slot when Karaoke is repeated on Channel 4 at 10pm on Monday.
It will be followed by Omnibus, documenting the history of the Comic Relief charity on its 10th anniversary.
Channel 4 claimed innocence yesterday. A spokesman said: "BBC1 has chosen an extremely popular documentary to put against us on Monday, about 10 years of Comic Relief. Potentially it's the most popular Omnibus in the run. Apocalypse Now has been seen many times and we brought the film forward because it is so long. I don't think the BBC has done us any favours."
The BBC appeared to be unfazed. "Channel 4 has an obligation to run an alternative," a spokesman said.Reuse content