Mark, meanwhile runs a busy eventing yard at Queenholme Stables in Leicestershire with his wife Tanya.
Their nine-year-old daughter Tabitha is now making a name for herself in show jumping, while also fearless on the hunting field with her father who is field-master with the Quorn Hunt.
"Tabitha is blessed as Mark has bought her some super ponies, but I actually learned to ride on a donkey," Gillian remembers. Her father Bill Cairns bred Shorthorn cattle and was good friends with Harry Watson, father of world eventing silver medallist John and grandfather of Olympian Sam Watson.
Eventing has been in the blood of these two families ever since.
As their sons began to find their feet in their chosen professions, Gillian and Johnny also found time to enjoy their horses again, but now at a different level, as breeders.
It was not by choice, however, following a serious car accident that was to sadly end Gillian's career in the saddle. It was also then that she pursued a different passion as an official with the FEI.
Having first learned the ropes as a national steward at Blarney Castle, for the past 20 years Gillian has officiated as a Technical Delegate in eventing at many of the world's top events, including London 2012 and the World Equestrian Games in 2014.
In addition she always enjoys her annual outing to the Dublin Horse Show where she is an official steward in the Main Arena for the duration of the week, while also being a member of the equestrian committee.
"I have the late, great Tommy Brennan to thank for getting me that stewarding gig," she said.
"During the spring and summer I am on the road non-stop at events across Europe and the States, but Johnny stays at home to hold the fort and look after the house and small herd of sheep. We've also been lucky to have bred some nice horses over the years, one of the most successful being Step In Time," Gillian recalled.
By Step Together out of the home-bred Cruising mare Festival Cruise, the gelding was ridden by Mark throughout his career and represented Ireland at Badminton in 2010 and at the World Equestrian Games the same year.
Mark also rode the grand-dam Festival Time up to three-star level, while Gillian's former dressage horse, the stallion Sailorman, comes from the same prolific family. He has numerous youngstock now competing in the UK with Mark and Tanya.
A veteran of the sport at 43, next week Mark will be making his third appearance at Olympic level, having also campaigned at Athens with Drunken Disorderly and in London with Coolio where the Irish team placed a credible fifth.
For Rio he rides the 10-year-old mare Jemilla and joining him on the team will be Olympic rookies Padraig McCarthy (Simon Porloe), Clare Abbott (Europrince) and Jonty Evans (Cooley Rorke's Drift).
Having officiated at London four years ago, on this occasion Gillian has decided not to fly down to Brazil, instead opting to stay at home and cheer on her son Mark, thanks to her other John, on FEI television.
"It must be rather unique to have one son competing and the other doing the commentary, but sadly I won't be there too."
"For me it's just too far to travel for only a few days and to be honest I have a lot going on here with upcoming events between Blenheim, the Millstreet International and Boekelo.
"I am also on the appeals' committee for the World Young Horse Championships at Le Lion d'Angers and on top of that I am scheduled to do a refresher course with the FEI."
As a keen dressage enthus ast and former chairperson of Dressage Ireland, it is incredible that Gillian also finds time to oversee competitions as chairperson of the Eastern Region of DI and as a committee member of the National Eventing Championships.
"At this time of the year I practically live out of my suitcase, but when I am home over the winter I do try to reclaim the garden, or what's left of it, before it all starts again next February," she concluded.