'Diana: The Witnesses in the Tunnel' was watched by 3.8m viewers and took a 16.6% share of audience, according to unofficial overnight figures.
Almost 4m viewers is a sizeable audience for a documentary, but Channel 4 will feel disappointed the programme did not pull in more viewers following acres of free publicity in the media and a favourable slot in the schedules.
Earlier in the week, Princes William and Harry pleaded with Channel 4 to remove images of their late mother from the documentary, but the broadcaster stood by its decision to air the documentary in its entirety.
The documentary was aired in a one-hour slot immediately before 'Big Brother', but live coverage of England’s crucial Euro 2008 qualifier against Estonia live on Sky Sports 1 and 'The Apprentice' on BBC One gave Channel 4 strong competition.
'The Apprentice' was watched by 6.2m viewers and a 27% share of audience.
'Big Brother' once again failed to scale the heights of the last series, with last night’s instalment attracting just 3.7m viewers and a 19.6% share of audience.
The eighth series of 'Big Brother' has lost more than 2m viewers in a week and average ratings are down 15% on the last series.
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