THE finale of chilling drama The Secret, depicting the murders carried out by Colin Howell, came to a conclusion with millions of viewers seeing the killer finally confess to police.

Viewers have been gripped by the four-part series dramatising one of the north's most shocking murder cases.

The first episode of the drama earlier this month drew in a massive 5.8m people, equating to a 23 per cent share of the overall audience.

An average of 5.5m have tuned in to the series, ITV said.

The broadcaster has faced strong criticism of the drama with some relatives of the victims, including Colin Howell's daughter Lauren Bradford, revealing how they have been re-traumatised by the series.

Tonight's final episode, broadcast just a day after the 25th anniversary of the shocking murders of Lesley Howell and Trevor Buchanan, was expected to draw in similar high figures.

Viewers, many of whom took to Twitter to voice their opinions on the final episode, watched as justice was finally served on Howell.

It's scary how he thought that God had forgiven him and it was grand that he murdered two people #TheSecret

— aisling(mully)? (@aislingmulcair1) May 20, 2016

The series has followed the devout Christian and his Sunday-school teacher lover Hazel Stewart, formerly Buchanan, conspiring together to kill their spouses.

For almost 20 years, their deaths were treated as suicide when they were found dead in a fume-filled car in Castlerock, Co Derry.

Killer dentist Howell and his lover Hazel believed they had got away with the gruesome double murder.

The series finale last night picked up the story as Howell's life had begun to fall apart following the tragic death of his son Matthew, with his guilt leading to him to confess his crimes.

It's all kicking off in the last episode of #TheSecret nail biting stuff!

— Vivien Reid (@VivienReid) May 20, 2016

The last episode of ITV drama, based on the book by veteran journalist Deric Henderson, saw Howell finally confess to police.

Viewers watched as Howell, played by Coleraine actor James Nesbitt, admitted the truth to police and in turn implicated his former lover Hazel.

#TheSecret I don't know which is more terrifying, the power of James Nesbitt's performance, or the fact that it's based on a real man

— Ghost (@Ayorkshireghost) May 20, 2016

The episode focused on the murder trial with Howell sentenced to serve a minimum of 21 years after admitting to killing his wife and Mr Buchanan.

Howell's evidence in the witness box led to Hazel, played by Dubliner Genevieve O’Reilly, also being found guilty.

Labour MP Louise Haigh raised concerns about the impact on the families of the murder victims in the House of Commons last week.

She said that the "re-telling of The Secret has brought untold trauma to the families connected to these tragedies".

The broadcaster was also accused of failing to give the family of one of the murder victims a preview of the controversial episode.