The two of them had travelled separately from Ireland for volunteer work, building homes in poor areas. But they did not meet until the end of their trip when they joined a diving expedition to see sharks.
"I believe everything happens for a reason. It was amazing helping to build homes for the poor but I'm very lucky, too; I met the guy I'm going to marry," said Sarah (31).
Will (33), a Dublin-based barrister, said: "Sarah was next to me in the cage going underwater. We hit it off straight away."
"Fear of great white sharks brought us closer together," joked Sarah.
Will had spent considerable time as a volunteer with the Niall Mellon Township Trust in South Africa. Sarah had decided to help the charity's 'building blitz' in 2007 as her sister Claire worked full-time for the charity.
Both Will and Sarah were so busy they did not meet during the week they spent working on the building site. Sarah believes it was fate that brought them together in the cage.
The couple got engaged recently, after Will approached Sarah's famous father Gerry (62) and her mother Helena at the family home in Ardglass, Co Down, to seek their blessing.
Despite being a giant of broadcasting in Northern Ireland, Gerry always put his future son-in-law at his ease when welcoming him to their home, said Will.
Gerry currently has a Saturday afternoon radio show on BBC radio. As the North's answer to Gay Byrne, he hosted several of his own shows on UTV over many years.
Sarah is currently manager of the Vera Wang bridal boutique at Brown Thomas in Dublin. She said: "I've loved my job. It's a lovely experience to see a woman falling in love with the dress she will wear at her wedding.
"I haven't chosen my own just yet but it will, of course, be a Vera Wang," she added.
Sarah believes she inherited the performing bug from her parents -- her mother was a folk singer and "Dad has always been supportive of whatever I've done," she said.
Sarah worked as a ballet teacher during her student years and worked as a professional actress for three years.
She toured Ireland with theatre productions and had a small part in the BBC serial Murphy's Law, starring James Nesbitt.
She joined Vera Wang to supplement her acting income but was quickly offered a full-time managerial position and opted for the security of the new position.
Will, a native of Clonakenny, near Roscrea, Co. Tipperary, was awarded a masters degree in international trade at the University of Limerick and travelled the world before qualifying as a barrister in Dublin.
The week-long Niall Mellon Township Trust 2011 'building blitz' begins on November 13, when 750 volunteers will travel from Ireland to build more homes for the poor.