Britain's Got Talent hosts Ant McPartlin and Dec Donnelly opened the show with an apology on Wednesday night, after a moment during the previous episode.
The pair brought attention to someone swearing on the show and apologised, before Ant identified the culprit.
Judge Bruno Tonioli was mortified to realise he'd been caught out, but as Ant and Dec exposed him there was booing from the audience.
Viewers tuning in had actually heard Bruno swear during Tuesday night's live show, believing they heard him shout "f***ing hell".
It went without mention though until Wednesday, when Ant called for a moment of silence so he could address it and apologise.
He said: "Now before we carry on, we have to just say sorry if you heard a bit of choice language on this show last night."
Ant then pointed at Bruno and Dec gave him side eye, but Bruno began looking around as if he didn't realise it was him.
As Ant said: "There will be none of that this evening," Bruno gasped and looked shocked as he stared at his fellow judges.
Dec then added: "We're not looking at anybody... right anyway," and Bruno held his head in his hands."
As Ant raised the issue though and continued to call out Bruno, the audience began booing and it got louder and louder.
It wasn't really clear if the crowd was booing Bruno over his language, or if they were booing Ant and Dec for telling him off.
The moment happened as Daredevil Andrew Stanton had everyone talking, as his "sick" semi-final act had viewers forced to look away from their screens.
The contestant pulled off a series of gruesome tasks for his latest performance, from sword swallowing and sticking giant springs up his nose, to dragging a truck along the stage using hooks attached to his eye sockets.
As Bruno stepped into the truck, he turned to Simon and said something which sounded like: "F***ing hell Simon, not again."
The moment did not go unnoticed, and one fan tweeted: "Bruno just said 'f***ing hell Simon, not again'," as a second said: "Did he just say f***ing hell???"
Another said: "I thought I heard Bruno swearing to Simon on stage about the act f***ing hell simon not this again or something along those lines."
Meanwhile on Tuesday, Viggo Venn and Olivia Lynes were the two acts revealed to have made it through after a public vote and a judges vote in the second semi-final.
First to be confirmed for the final was comedy and dance act Viggo, who shared his love for Hi Vis jackets - before getting everyone on their feet.
Despite not impressing everyone during the first audition, the act won the judges over this time as Alesha and Simon both confessed they loved his act.
The judges even claimed it was the best act of the night, and were thrilled when he made it through to the final based on the public vote.
Olivia then had to face fellow top three act Johns’ Boys, a choir group, as the judges were asked to choose which act to send through.
While Bruno saved Johns’ Boys, Simon, Amanda and Alesha all picked young singer Olivia which left her in tears.
Meanwhile, on Monday it was dancer Musa Motha and singer Amy Lou who won the first Britain's Got Talent semi-final of the series.
Talented dancer Musa, 27, was sent straight through to the final by viewers, so it went down to the judges' vote.
Ukelele musician and school teacher Abi Carter-Simpson and sunbed receptionist-turned-singer Amy Lou went up against one another.
As the judges struggled to decide, it went to the public vote and Amy Lou came second in the public vote.
There will be 10 acts in total in the live final on Sunday.
Britain's Got Talent's live semi-finals air all this week at 8PM on ITV1 and ITVX.
