CHICAGO - Former first lady Michelle Obama and former President George W. Bush have often been seen seated together at events.

Mrs Obama, 53, embraced Mr Bush at the opening ceremony for the Smithsonian National Museum of African American History and Culture last September. The photo of the affectionate moment went viral.

The New York Times called it "the embrace seen around the world".

The friendship is surprising to many given their political differences, and age difference but Mr Bush told People magazine in an interview posted on Wednesday (March 1) that he was genuinely fond of Mrs Obama.

Why?

"She kind of like my sense of humour, I guess," he said in the interview. "Anyone who likes my sense of humour, I immediately like... We just took to each other."

After putting down his executive pen, Mr Bush, 70, picked up a paint brush - and the hobby has become something of a career, AFP reported.

An exhibition of his oil paintings depicting US military veterans opens on Thursday (March 2) at the former president's library in Dallas.

The collection, on display at the George W. Bush Presidential Center in Texas until October 1, features 66 portraits and a four-panel mural.

Mr Bush's paintings pay tribute to the nearly 100 wounded or traumatised personnel who he has known personally since leaving the White House in 2009.

As the 43rd US president, Mr Bush had commanded the US military members, who all served in the wars he launched in Iraq and Afghanistan following the attacks on September 11, 2001.

The former commander-in-chief released on Tuesday (Feb 28) a book titled Portraits Of Courage: A Commander in Chief's Tribute to America's Warriors, which includes images of the portraits and the veterans' personal stories.

Mr Bush said he wanted to use the paintings and book to highlight the veterans' struggles with post-traumatic stress and the transition to civilian life.

"They're stories of courage, injury, recovery, willingness to help others," Mr Bush said during a Wednesday forum at the Reagan presidential library near Los Angeles, as part of his book promotion tour.

"And I also wanted to highlight the invisible wounds. That's my biggest concern."

Mr Bush's book has already shot to the top of Amazon's best-seller list, and the former president plans to donate profits from its sale to his presidential center's work aiding veterans.

He said the paintings would not be sold in his lifetime, but would be endowed to his foundation.

Matt Amidon, deputy director of the Military Service Initiative at the George W. Bush Institute, said the veterans have found it "incredibly meaningful... to have a former commander-in-chief to take the personal time to paint each one of them."

All-but-retired from public life, Mr Bush spends most of his time at his Texas ranch, where he first started painting in 2012.

He was inspired to explore his artistic side by famed former British prime minister Winston Churchill, who also painted in retirement.

"I basically said, what the hell, this guy can paint, I can paint," Mr Bush told a laughing audience at the forum, adding that it helped him stay active in retirement.

He kept his hobby a secret at first, but in 2014 unveiled 30 stylised portraits of heads of state he knew as president - all painted from photographs.

The distorted and sometimes only vaguely recognisable faces of people such as former British prime minister Tony Blair, Russian President Vladimir Putin, German Chancellor Angela Merkel and former French president Nicolas Sarkozy, attracted some withering criticism, panned as "naive" or "clumsy".

Others praised what they saw as the "high amateur" work of someone who, although not formally trained, had clearly studied some art history and painting techniques.

Mr Bush admitted during the forum that those earlier efforts lacked confidence.

"There's not much expression in it," he said, adding that he believes he has since evolved as a painter.

His new portraits - clearly more accomplished works - show greater mastery over the art.

The former president, who referenced impressionism in describing his work, said he was originally not very interested in art.

But since taking up painting he said he has come to see the world in a new light.

"I see colors and shadows that I never did before. I see the sky differently," Mr Bush said.

"It has changed my life to the better."

Mr Bush's idea to paint a portrait series of veterans came after his art teacher saw his collection of world leaders and suggested the former president next paint people outside the spotlight.

As with the world leaders portraits, Bush worked with photographs and spent a year on the artworks.

While other US presidents have taken up painting in retirement, Mr Bush is thought to be the first to paint portraits, AFP reported.

He said his current project is a six-foot tall self-portrait.

"It's a fascinating experience," he said.