The storyline prompted 200 complaints when it was introduced in September
Nearly 10 million viewers tuned in to watch the climax of the EastEnders child abuse story on the BBC One soap.
Fans of the show have watched as character Tony King, 33, has seduced his underage stepdaughter Whitney Dean.
Tuesday's dramatic episode, which attracted 9.9 million viewers, saw Tony's fiancee Bianca Jackson discover the affair and call police.
The BBC has said the show's writers worked closely with the children's charity, NSPCC.
In July, when the storyline was announced, a BBC spokeswoman said producers would be seeking professional guidance to ensure the subject was "accurately and sensitively portrayed".
In September, the storyline prompted more than 200 complaints when it first featured in the soap.
Fans of the show have seen Tony, played by Chris Coghill, continue his relationship with Whitney, played by Shona McGarty, while living under the same roof as Bianca, played by Patsy Palmer.
He led his stepdaughter to believe that, once she turned 16, they would leave Walford and live in Spain together.
Their secret relationship was uncovered when Tony refused to leave and Whitney told Bianca she was in love with him.
Figures for the episode were higher than those for the greatly-anticipated return of Bianca and ex-husband Ricky Butcher - played by Sid Owen - which attracted 9.7 million viewers.