'Discreet location' Barack Obama sought in the White House

Former President Barack Obama during his last news conference of his presidency in the Brady Press Briefing Room at the White House. Photo / Getty Images

There's a secret Barack Obama hid during his presidency in the White House that he's finally confessed to.

The former US president revealed the bad habit in his new memoir out this month.

For years people had speculated whether Obama had quit smoking - which he promised his wife Michelle he would do before he campaigned for president.

He'd never been caught or photographed with a cigarette but people had spotted nicotine gum on his desk.

Now Obama has revealed he smoked eight or nine cigarettes a day in the White House and only quit when his daughter Malia caught him.

In the 768-page book titled A Promised Land, Obama admits the stress of being president led him to finding a "discreet location to grab an evening smoke".

After Malia "frowned" after "smelling a cigarette on my breath", he said he quit smoking by "ceaselessly" chewing nicotine gum.

He also details how his time in the White House took a toll on his marriage, in a copy of the memoir obtained by CNN.

"Despite Michelle's success and popularity, I continued to sense an undercurrent of tension in her, subtle but constant, like the faint thrum of a hidden machine," he writes.

Former President Barack Obama waves as he arrives for a campaign rally for Joe Biden. Photo / AP

"It was as if, confined as we were within the walls of the White House, all her previous sources of frustration became more concentrated, more vivid, whether it was my round the clock absorption with work, or the way politics exposed our family to scrutiny and attacks, or the tendency of even friends and family members to treat her role as secondary in importance."

Obama said there were nights "lying next to Michelle in the dark, I'd think about those days when everything between us felt lighter, when her smile was more constant and our love less encumbered, and my heart would suddenly tighten at the thought that those days might not return".

Obama also details how Donald Trump promised an elixir for the "racial anxiety" of "millions of Americans spooked by a black man in the White House".

"It was as if my very presence in the White House had triggered a deep-seated panic, a sense that the natural order had been disrupted," he said.

"Which is exactly what Donald Trump understood when he started peddling assertions that I had not been born in the United States and was thus an illegitimate president."