The Stolen Earth
"The Beverly Hillbillies", "Green Acres", and "Petticoat Junction" shared a common universe, so crossovers were not uncommon. "Doctor Who" and "Torchwood" both take place in the same universe, and have had multiple crossovers, including Torchwood characters appearing in "The Stolen Earth" and "Journey's End". "Torchwood"s first series finale ends with the materialisation sound of the TARDIS, which is seen in "Doctor Who"s series 3 episode "Utopia".