The Crown creators are on the search for young actors with "a strong physical resemblance” to Prince William and Harry for the final series of the Netflix hit.
The successful candidates picked for the job will be playing "significant roles" in the drama.
A casting notice states it is seeking "two exceptional young actors" to play the dukes aged 16 to 20.
It reveals shooting for the final episodes of the show will commence in late August in the UK, adding: “No previous professional acting experience required.
“We are very experienced in providing a great deal of support for the young actors and their families through what they find is a uniquely rewarding creative process.”
The show is expected to return for its fifth series later this year, with a new cast taking over.
Screen veteran Imelda Staunton will replace Olivia Colman as the Queen as the drama moves into the 1990s, and Lesley Manville will portray Princess Margaret.
Elizabeth Debicki moves into the role of Diana, Princess of Wales vacated by Emma Corrin.
The series will reportedly dramatise her headline-making 1995 Panorama interview with Martin Bashir as well as other key events in her later life.
Writer Peter Morgan has previously confirmed the sixth series will be the last.
The casting call for the teen princes will be for the show's season 6, which will focus on their lives in the early 2000s.
Scripts and storylines won't be revealed ahead of the show's launch, but 2001 is when Prince William began his undergraduate course at St Andrew's university in Scotland - where he met his wife Kate Middleton.
It was also the year that Prince Harry earned his name as the Party Prince and was allegedly caught drinking alcohol and smoking cannabis.
Harry's use of booze and drugs resulted in Prince Charles taking him to a detox centre for heroin users as a scare tactic.
In 2002 the Queen famously stopped a criminal trial involving Paul Burrell, Diana's former butler, who was accused of stealing the princess's possessions.
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She had a "recollection" that the butler had told her that he was planning on taking the items - causing the case to collapse.
Virginia Giuffre claimed that in 2001 Prince Andrew sexually assaulted her and claimed she was trafficked to the prince by paedophile Jeffrey Epstein and Ghislaine Maxwell.
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