Bill Clinton appeared to be having a very good time with Michelle Obama at the opening of Barack Obama's presidential center on Thursday with one perfectly timed photograph capturing all the ingredients of a political rom-com.

The former president was snapped holding Michelle's hand while she wrapped an arm around Hillary Clinton.

The warm exchange quickly emerged as one of the standout images from a star-studded celebration that brought together four presidents, former first ladies, world leaders, celebrities and music icons in Chicago.

While there was nothing remotely scandalous about the moment, the picture was pure gold for camera crews, capturing the kind of unscripted interaction that often proves more memorable than the speeches themselves.

And it wasn't the only candid moment from the day.

Photographers also caught Clinton grinning broadly alongside the Obamas, sharing laughs with fellow VIPs and appearing thoroughly at ease as political rivals, allies and longtime friends reunited for the dedication of the sprawling Obama Presidential Center.

The gathering had all the trappings of a presidential summit crossed with a Hollywood gala, with the Obamas and Clintons joined by the Bidens, George and Laura Bush, former Vice President Kamala Harris and other household names.

The Clintons weren't the only ones enjoying themselves.

George W Bush appeared to spend much of the day cracking up with Michelle Obama, with one photograph capturing the pair doubled over in laughter. 

What the former president said remains a mystery, but it was clearly enough to leave Michelle howling while Bush looked equally delighted with himself.

Elsewhere, Joe Biden alternated between statesman and spectator. One photograph showed the former president sitting alone with his hands clasped and head bowed, looking deep in thought as the festivities swirled around him. 

Moments later, cameras caught him adjusting his trademark aviator sunglasses before taking to the stage.

The Obama daughters drew plenty of attention too. Malia and Sasha Obama were photographed together during the event, with Sasha's flowing red hair making her instantly recognizable among the sea of dignitaries and VIP guests.

Kamala Harris looked relaxed, dressed in a crisp white suit and sunglasses. The former vice president was photographed smiling broadly alongside her husband Doug Emhoff as supporters gathered around them.

The celebrity contingent was out in force too. Bono was spotted warmly greeting former House Speaker Nancy Pelosi, while former Canadian Prime Minister Justin Trudeau waited nearby with a grin as the U2 front man worked the crowd. 

One of the day's most unexpected images showed George W Bush chatting animatedly with musicians from The Roots backstage. 

The former president appeared fascinated by a giant brass sousaphone as he mingled with members of the legendary hip-hop band.

Several guests paused for selfies, including Oprah Winfrey, who happily squeezed into photographs with fellow attendees as the atmosphere increasingly resembled a reunion rather than a formal dedication ceremony.

Jennifer Hudson was seen gesturing dramatically to someone in the crowd, her hands spread wide as though delivering a punchline or telling a particularly good story.

Even Hillary Clinton appeared to embrace the relaxed mood. The former secretary of state was seen chatting warmly with Bono before later taking her seat alongside the former presidents and first ladies.

Guests could be seen celebrating from a golf cart as attendees were moved around the sprawling campus between events.

Former leaders and celebrities appeared to mingle like old friends at a family gathering.