The Crown season 4 is coming next month on Netflix. The streaming service has been sharing photos of iconic figures joining the royal drama ahead of its release. Some of the notable names appearing in the new season are Margaret Thatcher and Princess Diana.

In The Crown season 4, Gillian Anderson will play the role of the UK Prime Minister, while Emma Corrin portrays the beloved late Princess. While many are excited to see the next chapter of the royal drama, some fans noticed an error in one of the photos shared.

Back then, modern red buses weren't seen on the streets. However, an error in the background shot of Diana has been spotted, a view of a red bus. The rest of the set is full of vintage cars and scooters, but viewers took to Twitter after Netflix shared the photo.

Fans demanded an explanation as to why this thing went unnoticed in the photo. One fan wrote "not the Boris bus" in the background of Diana, while another one complained they can't even pretend it's the old-style Routemaster buses.

Meanwhile, some fans said that the shot could be just a misunderstanding. They pointed out that it may not be part of the clips from a certain episode. Instead, it's an on-set shot to teased viewers what's coming next. This is something that we're going to find out once the period drama returns on Netflix.

The Crown season 4 is set in the 1970s. The latest installment follows Queen Elizabeth (Olivia Colman) and her family searching for an appropriate bride for Prince Charles (Josh O'Connor), who's still unmarried in his 30s, to continue the line of succession.

The new season also sees a new tension is rising as The Queen and the nation adjust to the divisive policies implemented by Britain's first female Prime Minister. Moreover, the story looks at the Falklands War back in 1982, which generated conflict within the Commonwealth.

In addition to Colman, other returning characters in The Crown season 4 include Helena Bonham Carter (as Princess Margaret), Marion Bailey (Queen Mother), Tobias Menzies (The Duke of Edinburgh), Emerald Fennell (Camilla Parker Bowles), and Erin Doherty (Princess Anne).

Meanwhile, Anderson previously discussed playing Thatcher in the royal drama. She said that she's excited to join the cast and crew of the series, adding that it's an opportunity to play a "complicated and controversial woman."

In a related report, it was revealed that Imelda Staunton will play Queen Elizabeth in the fifth and sixth installments of the series. Elizabeth Debicki is set to play Princess Diana, while Lesley Manville takes the role of Princess Margaret and Jonathan Pryce as Prince Phillip.

The Crown season 4 premieres on Sunday, Nov. 15, on Netflix.