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On 4月21日, a number of things set in or relevant to the Doctor Who universe were released or published.
- 1973 - Episode three of Planet of the Daleks was first broadcast on BBC1.
- 1977 - Doctor Who and the Claws of Axos was released in paperback by Target Books.
- 1979 - Part four of the TV Comic story Size Control was reprinted as a Fourth Doctor story.
- 1988 - The novelisation of The Mysterious Planet was released by Target Books.
- 1994 - Legacy was first published by Virgin Books.
- 1994 - The novelisation of The Paradise of Death was released by Target Books.
- 1996 - Surprise Surprise! special was first broadcast on ITV.
- 2007 - Daleks in Manhattan was first broadcast on BBC One. Later, A New York Story aired on BBC Three.
- 2010 - DWDVDF 34 was first published by GE Fabbri Ltd.
- 2011 - DWA 214 was first released by BBC Magazines.
- 2011 - DWMSE 28 was first released by Panini Comics.
- 2016 - The Curse of the Fugue was first released by Big Finish.
- 2016 - DWFC 70 was first released by Eaglemoss Collections.
- 2017 - Who's Who was first broadcast on BBC One.
- 2021 - The Torchwood audio story Gooseberry was first released by Big Finish.
- 2022 - DWMSE 60 was first released by Panini.
- 2022 - The Torchwood audio story Infidel Places was first released by Big Finish.