The programme, which looked at the rocky road to romance for Prince Philip of Greece and the young Princess Elizabeth, pulled in an average audience of 3.4m and a 14.7% share.
It has been a royal week on television, with the first part of 'Monarchy: The Royal Family at Work' aired on BBC One earlier in the week, pulling in 6.7m viewers.
ITV1's 'Sold', which was scheduled in the same one-hour slot last night, 9-10pm, as the Channel 4 documentary, drew 3.1m and a 13.3% share. Last night's episode was the third of six episodes, in which Kris Marshall plays an estate agent.
'Sold' was bookended by 'I'm a Celebrity... Get Me Out of Here!', which pulled in 6.7m and a 28.6% share in the first one-hour instalment from 8-9pm.
The second installment, in which indie singer Cerys Matthews was evicted after engaging in a flirtatious relationship with former 'Eastenders' actor Marc Bannerman, was watched by 6.8m and a 31.8% share.
The former Catatonia singer was disappointed to discover upon leaving the 'I'm a Celeb...' camp that Bannerman, who was evicted last week, broke his promise to be present at the eviction.
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