The finale to the series, which aired between 9pm and 11.50pm, was reported to have made actor Jamie Bamber cry.
Elsewhere on the multichannel stations, Shameless logged 713k (9.8%) for E4 at 11pm, and 502k (3.7%) tuned in to watch a new episode of Horne And Corden between 10.30pm and 11pm, a drop of 305k from the first episode.
BBC One's Mistresses ended its run with 4.12m (17.6%) at 9pm. It beat ITV1's Holloway, which took 3.93m (16.8%).
Heston's Roman Feast, the fourth and final part of his series, managed 2.15m (9.2%) for Channel 4, with a further 291k (1.9%) tuning in on Channel 4+1.
CSI continued to perform well for Five, drawing 3.37m (14.4%) during the hour, although it failed to beat last week's series high of 4m. BBC Two was last for the hour, drawing 2.09m (9%) for Horizon.
Holby City was in the lead at 8pm, averaging 5.65m (24.3%) for BBC One during the hour. Its nearest competitor, ITV1's New Homes From Hell, drew 3.69m (15.8%).
BBC Two's Coast was watched by 2.12m (9.1%), while Five's documentary The Lion Cub From Harrods attracted 2.09m (9%).
Channel 4 was last for the hour, taking 1.94m (8.3%) for the penultimate episode of Supersize vs Superskinny.
Overall, BBC One came out on top in primetime with an average share of 22% to ITV1's 18.8%.Channel 4 was third with 8.2% (+1: 0.8%), followed by Five with 8.8% and BBC Two with 7.3%.
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Ratings data supplied by Attentional