The Real Housewives of Auckland have already been criticised for fat-shaming one cast member, but an upcoming episode of the show is set to cross the line even further.

In the sixth episode of the reality series, set to air on Tuesday, Julia Sloane is busted referring to co-star Michelle Blanchard as a 'n***er' whilst the women are enjoying a boat trip in Queensland's Port Douglas.

Former model Michelle is English, but is of Jamaican ancestry on her mother's side.

'She's not your boat n*****:' Julia Sloane reportedly makes a shocking racial slur towards co-star Michelle Blanchard on an upcoming episode of The Real Housewives of Auckland

The shocking scene happened off-camera, but the immediate aftermath was captured on film and is set to air on the show's next episode.

According to the NZ Herald, the slur is made when cast member Gilda Kirkpatrick asks Blanchard to help her up from below deck.

Julia, who is standing nearby, then reportedly remarks: 'She's not your boat n*****.'

Trouble On The High Seas! The incident takes place during a boat trip on Queensland's Port Douglas

A short preview for the episode shows Sloane in tears as the gravity of her actions dawn on her.

She also says in her on-camera confessional: 'It’s an old boating term. I should never have said it.'

The Spinoff reports that Blanchard reacts by throwing a glass of champagne in Sloane's face, before hurling the empty flute at the wall.

Stunned: A preview for the episode shows Michelle Blanchard looking shocked

Regret? Julia is also seen in tears after realising the gravity of what she has done

Sloane and her husband, investment banker Michael Lorimer, contacted lawyers to have the episode amended, but Bravo New Zealand has refused to back down.

According to NZ Herald, Lorimer said that the term 'wasn't intended to be racist,' and is a term he and his wife 'used occasionally in a tongue-in-cheek way' when sailing.

When signing on for the show, Radar Online reports that Housewives relinquish the right to control their image, even if their depiction is 'disparaging, defamatory, embarrassing or of an otherwise unfavorable nature.'

'It’s an old boating term. I should never have said it,' confesses Julia, who reportedly gets a glass of champagne thrown in her face after making the racial remark

Tears: Michelle's friend and co-star, Gilda Kirkpatrick, who witnessed the shocking remark, can also be seen looking distressed and overwhelmed in a preview of the episode

Sloane has since issued an official apology for the offensive slur.

'There is no excuse for using offensive words under any circumstances and I have learned from this foolish mistake,' Sloane said in a statement issued to NZ Herald.

The bubbly blonde adds that she is 'moving on' from the 'distressing experience.'

'There is no excuse for using offensive words under any circumstances and I have learned from this foolish mistake:' Sloane has since apologized for the racial slur

Blanchard has told The Spinoff that she was 'absolutely shocked' after hearing Sloane's insensitive remark during the cast trip to Port Douglas.

'I couldn’t believe what I was hearing. It took a while to sink in,' revealed the statuesque model.

She continued: '[Sloane] needs to own it. Don’t blame it on anybody else or make it out to be a lighthearted comment that you jokingly use, because you know what? It is not a lighthearted comment. It’s an offensive comment.'

'It’s an offensive comment:' Blanchard told New Zealand's The Spin Off

This isn't the first time that offensive comments have been made on The Real Housewives of Auckland.

On the show's first episode, Blanchard received criticism for 'fat-shaming' co-star Angela Stone after calling her a 'plus-size model' when they met over dinner for the first time.

When Stone became visibly upset over the remark and admitted that she was offended, a frustrated Blanchard responded: 'Sweetie, with tits like that you're not a normal size model. Get over it.'

'Are you a plus-size model?' Michelle was previously criticised for fat-shaming co-star Angela Stone in multiple episodes of the reality show

'Sweetie, with tits like that you're not a normal size model. Get over it,' snapped Michelle

The scuffle continued a few episodes later at Anne Batley-Burton's 'pussy party' to raise money for her cat charity.

While at the event, Blanchard criticised Stone's catsuit, which she deemed to be unflattering on the stylist's voluptuous frame.

'Pull your tummy in, sweetie!' she snapped at Stone in front of two other cast members.

The Real Housewives of Auckland airs on Bravo New Zealand, Australia's Foxtel, and on streaming app Hayu.