A man has been arrested on suspicion of vandalising a painting by the artist Mark Rothko, police said.
The 26-year-old was was arrested by Sussex Police - on behalf of the Metropolitan Police - at an address in Worthing after the valuable work was defaced on Saturday at London's Tate Modern art gallery.
The suspect was arrested on suspicion of causing criminal damage and is in custody at a Sussex police station but will be escorted to a London police station overnight by officers from Scotland Yard.
Earlier, Vladimir Umanets said he was responsible for writing on the painting. The wording on the bottom-right corner of the piece appears to read: "Vladimir Umanets, A Potential Piece of Yellowism."
Sources confirmed Umanets, originally from Russia, was the arrested man.
Umanets said he was not a vandal. He said: "Some people think I'm crazy or a vandal, but my intention was not to destroy or decrease the value, or to go crazy. I am not a vandal."
Umanets, who studied art, is one of the founders of "Yellowism", which he describes as "neither art, nor anti-art". "Yellowism is not art, and Yellowish isn't anti-art. It's an element of contemporary visual culture. It's not an artistic movement. It's not art, it's not reality, it's just Yellowism. It can't be presented in a gallery of art, it can be presented only in a Yellowistic chambers.
"The main difference between Yellowism and art is that in art you have got freedom of interpretation, in Yellowism you don't have freedom of interpretation, everything is about Yellowism, that's it. I am a Yellowist. I believe what I am doing and I want people to start talking about this. It was like a platform. It's good people are shocked about what happened, no-one is realising what actually happened, everyone is just posting that the piece has been damaged or destroyed or defaced. But I believe that after a few years they will start looking for it from the right angle. So that's why I did it."
He said he did not plan exactly which painting he would write on, but thinks he found "the perfect choice", and said he feels he may have increased the value. "To be honest, I do believe I increased the value, it seems probably ridiculous for someone but I do believe in this, I didn't decrease the value, I didn't destroy this picture, I put something new."
The gallery said it does not have a price for the defaced piece, but paintings by the Russian-born artist often fetch tens of millions of pounds.