The anti-media campaigner who interrupted SuRie's performance in the Eurovision final managed to invade the stage after climbing into the venue's camera run while being pursued by security.
Organisers the European Broadcasting Union said the man – believed to be a so-called "philosopher, activist and DJ" who goes by the name of Dr ACactivism – made his way to the stage via a bridge.
"He climbed into the camera run and reached the main stage via the bridge, pursued by security," said a spokesman.
"He was removed off stage after seven seconds and was questioned by police. We take security very seriously and an investigation into what happened is already underway."
The man previously stormed the stage during the final of The Voice in 2017 and the National Television Awards in January this year.
He grabbed the microphone from Britain's Eurovision entrant on Saturday night, before shouting about the "Nazis of the UK media".
SuRie remained on stage and clapped along to the music of her song Storm as the man was dragged away by security.
Dr ACactivism refers to himself on his website as an author of seven eBooks, and a post on his Twitter account from 10 May advertises his latest eBook called The Workings Of The UK State Mafia.
Hours before his Eurovision stage invasion he posted a video on Twitter that claims to show a journalist grabbing his neck.
Words across the video read: "Watch how journalists and Police of London use force to silence Independent Thinkers."
Dr ACactivism crashed the stage during the final of The Voice in April 2017, whilst holding up a piece of paper that was meant for viewers to read.
He was tackled by security before the audience had a chance to read the message.
The activist later claimed that the security staff almost broke his neck as they removed him from the stage.
One of Dr ACactivism's eBooks is called "My Struggle for the Freedom of Ideas Against the Corrupted Murdering Nazis of the Big Mainstream Media like the ITV: Murdering Nazis of the Big Mainstream Media."
In the book he touches on his stage invasion on The Voice in a section called "Whoever dares will be choked to death. This is the lesson that the ITV gave to me, Dr AC".
In January 2018, he tried to make it onto the stage at the National Television Awards while the nominees for the Bruce Forsyth Entertainment award were read out.
Presenter Dermot O'Leary was able to remove him from the stage without him making it on television.
Dr ACactivism posted a video on Twitter explaining why he tried to make it on stage at the awards ceremony, in which he said: "The artists and the journalists of the UK media are working with a philosophy that says control and oppress.
"So they control every institution that has to do with ideas, from the big media to social media, movie theatres, cinemas, book companies and so on."
He adds: "So I, Dr AC disrupted them for social justice, that is the freedom of ideas, the right of participation, and the right of being heard."
Graham Norton, who was the commentator for the BBC coverage of Eurovision 2018, said after SuRie's performance: "She was doing a brilliant job anyway."
He later added: "There was a stage invasion, SuRie coped incredibly well, I can't stress enough what a brilliant job she did, she must have been terrified."
The European Broadcasting Union offered SuRie the chance to perform again but she chose not to.
SuRie came 24th of the 26 entries in the contest.
The 29-year-old tweeted afterwards: "Well I've always said anything can happen at Eurovision.
"I'm so proud of my performance tonight. I gave it my very best.
"It's been an incredible experience for me. I am so grateful for everyone's love and support.
"The fans make Eurovision what it is; the biggest and the most inclusive and open celebration of music in the world."
More from UK
The competition was won by Israel's Netta, who sang her quirky dance number Toy.
Although acts of activism in the Eurovision Song Contest are rare, the competition does have a long history of political voting.
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