Gordon Brown, the former British Labour Prime Minister, is appearing before the Leveson Inquiry into UK media ethics today, along with Chancellor George Osborne.
Meanwhile, Conservative Prime Minister David Cameron is due to appear Thursday, during what Sky News called "most politically-charged week" of the inquiry sparked by phone-hacking at Rupert Murdoch's tabloid News of the World.
Another ex-prime minister, John Major, will appear Tuesday, along with opposition Labour Party leader Ed Miliband and his deputy, Harriet Harman, CNN reported.
Brown has been a harsh critic of media baron Rupert Murdoch, however London's Daily Telegraph pointed out that in 2008, Murdoch's wife, Wendi, and then News International chief executive Rebekah Brooks attended a "pyjama party" at the Prime Minister's country retreat, Chequers, hosted by Brown's wife, Sarah.
Murdoch has said relations broke down after The Sun switched its support to the Conservatives in 2009.
Murdoch told the inquiry in April that Brown had phoned him in an "unbalanced" state of mind and declared war on his media empire, the BBC reported.
Controversially, The Sun also disclosed that Brown's son Fraser was suffering from cystic fibrosis, sparking a claim that the information was obtained via phone hacking — which Brooks denied.
Cameron has been under pressure because of his close ties to Murdoch and Brooks.
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Osborne, meantime, is likely to be asked about the Conservatives' hiring of Andy Coulson, a former News of the World editor, as Cameron's chief of staff before his election to office, BBC reported.