EastEnders fans were happy when Mark Fowler Jnr made his Walford debut but we're not sure they're going to like this storyline…
Poor Mark and Courtney, they've been flirting, have admitted that they do have feelings for each other but they're unaware that they are in fact related and, err, how do we put this… brother and sister.
The pair first met on their way to Notting Hill Carnival and have since become close. And in last night's episode at Shakil Kazemi's birthday party, Mark admitted that he does like her.
Unfortunately the pair are unaware that they have the same dad – Grant Mitchell.
Back in 1995 Michelle Fowler and Grant Mitchell had a one-night stand and alas Mark Fowler Jnr was born.
But Grant has no idea that he has a son. Only Phil, Sharon Mitchell, Ian Beale and Martin Fowler know the truth and are trying to keep it under wraps.
But as the pair got closer Sharon and Ian rushed to stop them. Fans are left wondering whether the pair kissed.
This isn't the first time EastEnders has done an incest storyline, they previously had Lauren Branning and her cousin Joey Branning in a relationship even though they knew they were cousins.
And EastEnders fans took to Twitter to share their feelings about the Mark/Courtney storyline. Some viewers forgot that the pair are related:
"Watching EastEnders, hold on aren't that Courtney and Mark brother and sister?!?!"
"I just realised Courtney and Mark are half bro and sis #EastEnders"
Other viewers didn't seem keen on the taboo storyline.
One fan wrote: "Uh oh I hope we don't get an accidental incest story coming up between Mark Jnr and Courtney #eastenders"
Other people tweeted:
"Courtney and Mark don't know that they have the same dad? The writers better not think about doing what I think they might do #EastEnders"
"They can't do the Courtney and Mark thing on EastEnders eww too far"
And with Grant Mitchell returning to the show next week, we're sure it won't be too long until it's revealed that Courtney and Mark are related, but will it be too late for the couple's feelings?
What do you think will happen?
Let us know your thoughts on Facebook or our Twitter (@CloserOnline) page.