All alone in the middle of the Pacific aboard his 30-meter (98-feet) trimaran MACIF, the French sailor's heart skipped a beat.
Although his on-board satellite hadn't spotted any large obstacles in the area, an iceberg showed up on the side of his boat shortly after he passed New Zealand.
"It was the scariest moment of this race," Gabart told CNN.
"You don't know if it's a big one or a small one," said Gabart, who estimated the iceberg was about a mile from his multi-hull yacht when he spotted it. At that time, there was just four hours of daylight left.
"I was far away from any land, the closest land was the Antarctic. You are far away from any humans and safety. It's dangerous and if something bad happens in this part of the world, you could be in a tricky situation," he said.
27,859.7 nautical miles
His first, and only, encounter with an iceberg was one of a few blips in an otherwise near-perfect voyage, with the 34-year-old father-of-two crossing the finish line in the English Channel a few weeks later in a new single-handed around-the-world record of 42 days, 16 hours, 40 minutes and 35 seconds at his first attempt.
His yacht traveled a total distance of 27,859.7 nautical miles, at an average speed of 27.2 knots (50.4 kph) and a top speed of 39.2 knots (72.4 kph).
Gabart would sometimes sleep only two or three hours a day. In the last 24 hours, he didn't sleep at all as he chased down a record many had said couldn't be broken.
Gabart, a trained engineer who won the 2012-2013 Vendee Globe race as a rookie entrant, and also triumphed in the 2014 Route de Rhum, has now joined an elite group of just four sailors, including Francis Joyon and Thomas Colville of France and Britain's Ellen MacArthur, to have held the single-handed, non-stop around the world record.
"I am not sure if I would be able to do it again," Gabart said, when asked how he looked back on his achievement after almost a month on dry land.
"It still feels a bit unreal ... but I am very proud of what I did."
Although the Frenchman had expected a close race, he obliterated the previous mark, set in 2016 by Colville, by more than six days.
"People said it would be hard to break it, and I was saying this also," he said of Colville's record, which was set on his fourth attempt.
"And it was hard. (Several factors need to go your way) to break a record like this. You need to have a good boat, you need to sail well and you also need to have good weather, which means to be lucky. And clearly I was lucky to have this weather."
Sailing solo around the world non-stop -- widely regarded as the most difficult record to break -- requires meticulous preparation and hours and hours of training.
One of the few things you cannot prepare for are situations like encountering an iceberg.
"I'm training hard and working all year with all my team to try to reduce the risk as much as possible," said Gabart. "It's never zero, but trying to be close to zero."
"It was the first time I saw an iceberg in my life. I was just alone on a carbon boat, going quite fast so if you crash ... I'm happy to have done it because it's something exceptional, but during the situation it was not comfortable and it was a little bit too dangerous for what I want. I don't want to risk my life when I am sailing boats like this."
How long will record last?
Technological advancements mean Gabart's record isn't likely to stand for long.
His MACIF yacht, for example, had a bigger sail area and was wider than previous round the world trimarans, allowing Gabart to keep sailing even in lighter winds, according to Yachtingworld.com
"It will be hard to beat it again now, but someone will do it again, I think in a short time in the future," Gabart said.
"And probably they will break it by a few days because we have boats that are sailing faster and faster, and there is no reason that you can't do better every time."