Media mogul Rupert Murdoch was hit with a foam pie while testifying to a British parliamentary committee and a man was arrested, an AFP correspondent reported.
Murdoch's wife Wendi Deng, who was also in the hearing, leapt up and appeared to hit out at the unidentified man after the incident, in which the News Corp. chief was hit on the shoulder.
The hearing was suspended for 10 minutes.
The Guardian newspaper and Sky News named the attacker as a comedian called Jonnie Marbles.
In a message on his Twitter account shortly before the incident, he said: "It is a far better thing that I do now than I have ever done before #splat."
London's Metropolitan Police had no immediate information.
The incident happened at 4:54 pm (1554 GMT) as the Murdoch and his son James were about to face the last questioner, Conservative lawmaker Louise Mensch. Someone shouted "no, no, no, no!" as a man in a checked shirt approached the pair from their left and attacked Rupert Murdoch with the plate.
James Murdoch looked shocked by the incident but could not stop the attack, while Mensch had her mouth open aghast as the man hit the 80-year-old, who remained seated throughout.
He attempted to protect his head and took his glasses off. Foam could be clearly seen across his right shoulder.
An uniformed policeman rushed across to apprehend the assailant as a man shouted "outrageous!".
"The sitting is suspended for 10 minutes," chairman John Whittingdale said.
Police detained the attacker outside the room, who had white foam across his face and shirt. He was handcuffed behind his back and led away by a single officer.
Witness Andy Thompson, a member of the public from Vancouver, western Canada, said he saw the attacker lunge towards Murdoch holding a green bag with shaving foam in it.
When the session resumed, Murdoch was without his jacket.
Earlier, within seconds of the start of the session, two people stood up three rows behind them with signs reading "The People Vs Murdoch".
"Excuse me, can we not have that, please?", Whittingdale asked, before having the pair removed.