Rupert Murdoch promotes eldest son Lachlan Murdoch to be co-chairman of 21st century Fox and News Corportaion

Lachlan Murdoch will be co-chairman of Fox and News Corporation

Lachlan Murdoch, Rupert Murdoch and James Murdoch attend The Television Academy's 23rd Hall Of Fame Induction Gala at Regent Beverly Wilshire Hotel on March 11, 2014 in Beverly Hills, California (GETTY IMAGES)

Rupert Murdoch looks to have annointed his eldest son Lachlan as his heir apparent, promoting the 42-year-old to be his co-chairman at the top of both the media companies that the veteran mogul runs.

Lachlan Murdoch will be co-chairman of TV and film company 21st Century Fox and of newspaper group News Corporation.

Rupert Murdoch, who turned 83 two weeks ago, was previously sole chairman of both companies, after Fox's split from News Corp last July.

He hailed his eldest son as "a strategic and talented executive with a rich knowledge of our businesses", adding: "I'm very pleased he is returning to a leadership role."

Lachlan Murdoch held a series of senior roles within News Corp during his twenties but quit most of those roles when he was in his thirties, leading to speculation he had fallen out of favour.

Having spent most of his time in Australia in recent years, he will split his time between Sydney and New York in his new roles.

James Murdoch, Lachlan's 41-year-old brother, also got a promotion today - to co-chief operating officer at Fox, from deputy chief operating officer.

Rupert Murdoch described it as an "important role" for his son, who will have "direct responsibility" for the Fox TV networks in America and also for all the company's international TV interests, including its 39 per cent stake in BSkyB in Britain.

It means the younger Murdoch will be effectively overseeing Sky, two years after he quit as its chairman after investor dissent.

However, James Murdoch, who was widely regarded as the heir apparent until the phone-hacking scandal blew up, now appears to be less influential. He will report to Fox's other co-chief operating officer, Chase Carey.

James Murdoch is a non-executive director at News Corp but resigned all executive responsibilities after failing to get to grips with the hacking scandal while he oversaw the UK papers between 2007 and 2011.

Observers have long wondered about whom Rupert Murdoch would like to see take over from him as the fortunes of Lachlan, James and their sister Elisabeth, founder of TV company Shine, rose and fell.

Michael Wolff, the New York media commentator and biographer of Rupert Murdoch, said of today's shake-up: "I have always said that it doesn't matter to Rupert Murdoch who succeeds him just as long as the person is named Murdoch."

Rupert Murdoch, who recently divorced third wife Wendi Deng, has six children. Eldest daughter Prudence has little involvement in the empire while his two youngest daughters are of school age.