Throughout his 15-year rugby career, Brian O'Driscoll had never been in a situation quite like this.
Brought up a Catholic south of the border in the Republic, O'Driscoll joined Protestants and loyalists in attending a July 12 celebration in the small village of Loughall, Northern Ireland. His background immediately segregated him from the rest of the crowd, but the former Ireland captain was keen to extend a friendly hand.
Soon, pictures of O'Driscoll banging a Lambeg drum, a traditional instrument which has become associated with the Protestant, loyalist Orange Marches, surfaced on social media.
As he checked his messages, the reaction showed that the idea of a republican Catholic, even a figure as popular and respected as O'Driscoll, directly contributing towards such overtly unionist celebrations was extremely controversial.
The moment is shown in an upcoming documentary produced and presented by O'Driscoll called Shoulder to Shoulder, a film which examines what it means to be Irish and explores how an island still separated by borders, religion and politics is brought together by the sport of rugby.
"I thought it was important to culturally understand what being Irish meant to the Orange Order," O'Driscoll tells ESPN, ahead of the release of Shoulder to Shoulder on BT Sport on Oct. 12.
"There are so many intricacies to what being Irish is, and it means different things to different people.
"I understood the republican, Catholic perspective from growing up all my life like that, but what I was trying to discover was what culturally everyone is about."
O'Driscoll made his Ireland debut in 1999, one year after the Good Friday agreement brought an end to the bitter 30-year war called the Troubles. As the former centre only represented his country during times of peace, in the film O'Driscoll also meets the men who played for a united Ireland while their neighbours went to war.
What was extraordinary is that, like today, Irish players came from both sides of the religious and political divide but put aside their differences while other Protestants and Catholics, loyalists and republicans fought and killed one another.
"The commonality was playing in the Irish jersey," O'Driscoll says. "It didn't matter what your political or your religious beliefs were. Whether you were from the north or the south, you had to be united as a team against any opposition."
There are some incredible stories told by the great Irish players of the 1970s, 80s and 90s of an unrecognisable time; of dodging explosions in Belfast and escaping car bombs on the Irish border. O'Driscoll is often visibly struck by the recollections, and the idea of how different his life and career would have been had he been born 20 years earlier.
For O'Driscoll the standout moment from the filming process of Shoulder to Shoulder was listening to the stories of Willie John McBride, a giant of the Irish team of the 1970s who represented his country 63 times and made 17 appearances for the British & Irish Lions.
McBride was working as a bank manager in Belfast on the day of the Bloody Friday bombings in 1972, when over 20 IRA bombs were detonated in the centre of the city. McBride, now 78, describes how he was told to evacuate the building and was forced out onto the streets. With explosions going off all around him, he did not know where the next one would come from.
"I was trying to get a sense of how harrowing and frightening that would be, and hearing it from John and listening to what he was thinking in that moment was a real eye-opener," O'Driscoll says. "All he could really think of was sheer panic.
"We got some great interviews and hearing what rugby meant to players like John, and what those occasions and scenarios meant to them, I think there are some good stories to be told in all of it."
Shoulder to Shoulder, the next installment in the BT Sport Films series, premieres at 10pm on Oct 12, on BT Sport 2. Watch on TV and via the BT Sport App. btsport.com