The 24-year-old Ireland flanker left his tough guy image on the pitch when he popped the question to childhood sweetheart Suzanne Flanagan on a Miami beach.
His meticulous preparations ahead of the surprise proposal, which included "always keeping the ring on my person", culminated in him getting down on one knee in the Florida sunshine.
And his plan was rewarded in style when the 25-year-old dentist from Jordanstown, whom he started dating as a 17-year-old schoolboy at Belfast Royal Academy, said yes.
"She was overly excited when I asked her to marry me on July 14 - and quite surprised too," the 26 times capped international revealed. "I think she knew that I was going to ask her at some point, but she didn't know when it would be or how I would do it."
The full-time professional player from Ballinderry whisked his bride-to-be off to America on his return from South Africa after a three-week rugby tour.
And, as you would expect from a seasoned sportsman, he went thoroughly prepared, having bought a sparkler for the special occasion ahead of the couple's summer holiday in America.
"We left for Miami on June 28 and we'd been enjoying ourselves and visiting a few theme parks in Florida before I asked her," Iain said.
"It had been on the cards. The ring had already been purchased beforehand and I had the proposal semi-planned out."
But was he not terrified that he might lose the ring before he got a chance to ask for Suzanne's hand in marriage?
"That was a worry, I admit," he said. "But most of the time it was on my person or stashed away in hotel safes. The night I ended up asking her, I didn't have a huge plan. It happened on a Miami beach after we had finished dinner.
"It wasn't overly thought out, but I got down on one knee and she said 'yes' at once."
The couple, who spent a further five days in the Sunshine State celebrating their impending nuptials, first began dating in school.
"We started seeing each other first when we were at Belfast Royal Academy -I was 17 and Suzanne was 18," said Iain, who is studying for a maths degree at the Open University.
"We stopped seeing each other when she went to Glasgow to study and I stayed in Belfast to play rugby, but we got back together again a year-and-a-half ago."
Iain said his parents, Gordon, a quantity surveyor, and Zoe, an occupational therapist, who are both in their 50s, were delighted when they heard the good news, as were his older brothers Stuart (31) and 26-year-old Richard.
"We didn't tell many people we were engaged when we were out there - just family and very close friends," he said. "But we've been drinking a lot of bottles of bubbly and celebrating with friends we've invited to the house since we've been back in Northern Ireland."
Now, the loved-up couple, who currently share a home outside Lisburn, are limbering up for a 2017 wedding once they finally settle upon date and a reception venue.
"There are wedding magazines everywhere," Iain said. "I didn't realise that there was so much to organise."
"It would need to be finalised sooner rather than later for my sanity."
The busy duo have also yet to pick a honeymoon destination.
"We haven't actually thought of anywhere yet, but maybe the Maldives or Mauritius, or somewhere like that," the rugby star told the Belfast Telegraph.