On my first encounter with identical twins Laviai and Lina Nielsen — not long after they had achieved matching A*/A/B results in their A-Levels — the intimacy between them was immediately apparent: giggling together over private jokes, finishing one another's sentences and making sure there were no errant locks of the other sister's hair that might ruin the photoshoot.
At that point, back in early 2017, they were university students with a dual dream that has since edged ever closer with each passing year - an ambition to reach the very top of the athletics world. That ambition now looms into view with the imminent arrival of this summer's Paris Olympics. Yet the highs and lows to get there have been innumerable.
Over the past few years, the 28-year-olds have won countless British and international medals, posed for the likes of Vogue and Elle magazine, moved their training base from north London to the United States, Austria and, currently, Denmark in the endless pursuit of perfection, and - most remarkably - battled multiple sclerosis (MS) that affects both of them in unequal measure. But their relentlessly cheery outlook has remained throughout, visible in the wide smiles rarely absent from their faces during interviews and their frequent video blogs.
This summer, the Nielsens hope to reach the sporting summit of the Olympics, where Laviai is aiming to contest the 400 metres and Lina the 400m hurdles. All being well, they will then join forces to compete together as part of Team GB's 4x400m squad.
If they achieve their aim, it would be an extraordinary legacy from the London 2012 Olympics - an historic event that took place in their home town. Back when the capital was confirmed as host city, the primary school both sisters attended barely two miles from what would become the Olympic Park was converted into a specialist sports school. For two young girls who loved nothing more than tearing about, the newly installed track in the playground was a godsend.
"We used to just do lap after lap after lap," Laviai told the Telegraph in 2017. "Our friends would join in… and then they would drop out. Literally the whole lunchtime we'd just do laps to see how far we could go."
They volunteered at those London Olympics, where Laviai had the unforgettable experience of carrying eventual heptathlon gold medalist Jess Ennis's kit, and within a few years the twins were making a name for themselves on the athletics circuit. But their progression was far from smooth. When Laviai won European junior 400m gold in 2014, Lina was not well enough to even try to qualify for the British team. It would take another eight years for her to publicly reveal that the problem was MS.
It had first struck in the form of sudden weakness in her left arm when she was only 13, but was misdiagnosed as a stroke - a common mistake in young people with the disease. A few years on, she fell flat on her face while warming up for a race and ended up in hospital for a week undergoing various tests. She was diagnosed with MS a month before her 18th birthday.
"I just remember bursting into tears in front of the doctor," she told me in a 2022 Telegraph interview that she was adamant would not be a sob story. "I felt like I'd been given a life sentence. He said it was chronic, incurable and I'd have it for the rest of my life.
"I told him about my running and I remember him saying: 'You might need to think about changing your lifestyle'. He said they didn't know how bad or good it would get. I cried for the rest of the day. I've never cried so hard in my life."
Incredibly, she did not even tell Laviai for two months, overwhelmed with guilt over the likelihood that her sister would share the disease. She was correct, although Laviai has never suffered major symptoms, unlike Lina who had successfully managed the issue for years until she was cruelly afflicted the night before the biggest race of her life at the 2022 World Championships.
The sisters have since controlled the condition through diet alone. "We're still deciding not to take medicine because we're not sure of the side effects," Laviai told the BBC earlier this year. "We've always been pretty good with our diet and nutrition, but after Lina's flare-up we've taken it even more seriously. So far it's all gone well."
Born to an Egyptian-Sudanese mother and Danish father, the sisters have gone from strength to strength since last October moving to Denmark, where their surname - one of the country's most common - is plastered on everything from billboards to buses. They both ran faster than ever during a 2024 winter indoor season in which they combined to help Britain win world indoor 4x400m gold.
The hope is that it was just the warm-up act before the big one at this summer's Paris Olympics. Should they make it, they will most certainly have earned it. "People talk about having to travel a rocky road with lots of highs and lows," said Lina, who is also a professional yoga teacher. "But I feel like we've climbed mountains to be where we are."
Ben Bloom is a freelance writer who began his journalism career as a local news reporter before focusing on sport in 2012. He spent 11 years at The Telegraph, where he wrote on a wide range of sports, leading the paper's coverage at three Olympic Games. His work saw him nominated for a British Sports Journalism Award.