Strauss was commentating for Sky Sports on the MCC versus Rest of the World match at Lord's when he made the offensive remark about Pietersen.
Sky Sports had been on a break but viewers of Fox Sports in Australia, who take the channel's commentary, heard the exchange between Strauss and Nick Knight. Strauss said that he apologises unreservedly, particularly to Pietersen, adding that he is mortified and profusely sorry, the BBC reported. Sky Sports had earlier apologised for the language used by Strauss.
English sports writer and radio broadcaster Pat Murphy said that they understand Strauss thought that he was off air but the comments were broadcast in Australia.
Murphy said that apparently during an advert break, Strauss was talking to Knight, and referred to Pietersen in very derogatory terms.
Strauss had been captain of England when Pietersen was dropped for sending derogatory text messages about his teammates, Strauss in particular, to members of the South Africa team in 2012.