Meghan Markle and Prince Harry's interview with Oprah Winfrey was watched by an average of 11.1 million people in the UK.
The one-off special also had a peak of 12.4 million viewers, according to figures from ITV.
The two hour programme aired on ITV from 9pm after first being broadcast on CBS in the US, drawing in 17.1 million watchers across the pond.
It's overtaken The Masked Singer's February final, which was watched by 8.6 million, as the biggest TV show of the year in the UK.
Watch: The key revelations from Meghan and Harry’s Oprah interview
Boris Johnson's COVID-19 address to the nation on 4 January is still the most watched broadcast of 2021 which reached an audience of 15.6 million on the BBC alone, while also being shown on the BBC News channel, ITV, Channel 4 and Sky.
The explosive interview saw the couple claim a member of the royal family made a racist comment about their son, while Markle said she had suicidal thoughts at the height of her crisis in the monarchy but that attempts to reach out for help were turned down.
The Duke and Duchess of Sussex said there had been “concerns and conversations” before their first child Archie was born about his skin tone and “what that would mean or look like”.
They did not disclose the identity of the person who made a remark, but in a follow-up interview on CBS Winfrey told presenters it was not the Queen or her husband Prince Philip who were involved.
She told CBS This Morning: “He did not share the identity with me but he wanted to make sure I knew, and if I had an opportunity to share it, that it was not his grandmother or grandfather that were part of those conversations.
“He did not tell me who was a part of those conversations.”
The palace has not yet responded to claims made by the couple.
Oprah with Meghan and Harry is available to watch on the ITV Hub.
Watch: Piers Morgan storms off Good Morning Britain