When he started his career, in 2011, he was hailed as the next big thing in Belgian cycling - the first to be handed that poisoned chalice of successor to Tom Boonen.
Life, however, has thrown a lot at Van Keirsbulck since his teenage years ended and, as he reels off a list of the hardships he has faced, it's easy to understand why that potential has so far been left unfulfilled.
There's nowhere else to start than the death of his girlfriend, Emilia Bonami. A couple for two years, they would do everything together, until one tragic moment on June 27, 2011. It was the day after the Belgium national championships, Van Keirsbulck had just signed a new contract at Quick-Step, and the pair were on their way to his grandfather's house for a celebratory barbecue. Since she had an exam the next day, Bonami was travelling separately, in her own car directly behind Van Keirsbulck.
"It was a stupid accident," Van Keirsbulck recalls. "I think she wanted to grab something next to her, so she took her seatbelt off, and then she went a little to the right, over the bike path, and there was a little bump, and I think she panicked and she swerved, and on the other side of the road a motorbike was coming. They crashed and then she hit a tree. I saw it all happen in my mirror."
Van Keirsbulck scrambled to free her from the wreckage, but there was nothing to be done.
"She died in my arms actually," he adds.
Van Keirsbulck's life changed dramatically after that. He was still coming to terms with the death of Wouter Weylandt, who died in a crash at the Giro d'Italia just seven weeks earlier. The pair were close and Van Keirsbulck had been one of the riders who carried the coffin at the funeral.
Tragedy piled upon tragedy, there was a heavy emotional toll.
"Straight after the accident I was ok. I was back on the bike quite soon. I wanted to win a race for her, and after one month I won one, but after the season finished I went into a black hole," he says.
"It was not good for me. You don't train anymore because the season is finished, and you start to go out. You don't want to be home because you're thinking about it too much. You want to escape from everything. So I went out and did whatever I wanted. It wasn't only drinking, it was just a need to get out of the house because if I stayed in I would go crazy."
Finding it difficult to open up to his family, Van Keirsbulck eventually sought professional help. Counselling helped him "to see things normally again" but, by the time he was doing so, his priorities had shifted.
"You start living differently after that. You start thinking, 'what the fuck, life goes so fast'. Then I started to enjoy my life a bit more. Outside of cycling you have a life, and that period I did too much outside of cycling. I liked to enjoy more things. It took a few years to reset my mind."
Van Keirsbulck tuned up to the pre-season training camps overweight and there was the added distraction of being spotted out with model Larissa De Castro, who at the time was 'Miss East Flanders'. Coming seven months after Bonami's death, the story caused a stir, and even as the relationship solidified and the pair became a long-term item, Belgian magazines would run photoshoots of De Castro alongside stories about their sex life.
With cycling far from front and centre of his mind, the 2012 and 2013 seasons were forgettable, though things looked like they might be back on track in 2014 as he won the Three Days of De Panne and a stage of the Eneco Tour. In 2015, however, there was more disruption. A back injury ended his season in June, and he ended up having to undergo two operations. He was just recovering from the second - along with a split from De Castro - when another car accident occurred.
"I was a little drunk," Van Keirsbulck admits, recalling how he left a nightclub with teammates in the early hours of the morning, before crashing his Audi RS6 through a traffic sign and into a tree. Fortunately, no one was hurt - only his reputation.
"In Belgium it was in all the newspapers: 'Quick-Step rider crashes his car.' I was the bad guy in the eyes of everyone."
That incident nearly cost Van Keirsbulck a contract extension. In the end he re-signed with Quick-Step for another year, but rode a reduced spring Classics campaign, and where he did ride he was mostly deployed as a workhorse for controlling breakaways in the first half of the races.
That's why, for 2017, he decided to leave Belgium's premier cycling squad to drop down to the Pro Continental ranks with Wanty-Groupe Gobert, where he'd have the chance to pursue his own objectives in the business end of races. It looked like an inspired move as he won Le Samyn in March, but the rest of that spring was derailed when his father was diagnosed with leukemia.
"It was E3-Harelbeke, and I saw my sister beyond the finish line. I stopped and she was crying. She said 'Dad's in hospital and we need to go straight away'. That wasn't easy to hear. But he didn't want me to be there - he said I needed to do the Classics. I said 'you're my dad, I don't want to lose you'. Things are under control now but for those weeks at the classics my mind was a bit busy."
Summing up, Van Keirsbulck, without self-pity, states: "I've had a lot of problems.
"I think that's a big part of my career already. It's already a lot of things. People…they know it but they forget it after a while. They say 'he is not so good', but if you see all the things in my life, it's a part of who I am now. If I didn't have all those things I would be a few steps better in the sport than I am now."
'I still have potential'
Van Keirsbulck arrives at CCC with renewed optimism and motivation. It's his second second chance, if you like. The move to Wanty was supposed to be the first, but things never really worked out, and not just because of his father's health. Though he insists the chance to 'race' again - rather than "just pulling" - reignited his love for the sport, that freedom afforded at the Pro Conti outfit proved a double-edged sword.
"At Wanty I could do my own thing, but the problem at Wanty is that everyone can do his own thing," he says. "There was no structure with the tactics. The manager would say to someone, 'you stay with Guillaume today', but the race starts and you never see the guy. They are all good guys but everyone's thinking about themselves, everyone wants to go to a bigger team and to show what they can do - that's the problem with smaller teams. Here [at CCC] if you don't listen to the orders, you're not going to race the next race."
Van Keirsbulck also found it frustrating, and slightly baffling, to have 'Wanty amateur' shouted in his face. "Wanty didn't have that respect the in bunch. Guys who don't know you from before, especially young guys in WorldTour teams go straight into a big team and think they are the man. Wanty amateur… what the fuck, are you crazy?"
Van Keirsbulck will encounter no such problems of status in 2019. Back in the WorldTour, the top tier of the sport, he will be riding alongside one of the very best Classics riders in the world in Greg Van Avermaet. It was the Olympic champion who personally requested he join, as they set about rebuilding after the sponsorship struggles that saw more than half the original BMC roster leave.
The two knew each other but weren't close friends, and after stage 4 of the Tour de France, where Van Keirsbulck had been in the breakaway, he received a direct message on his Instagram account. In it, Van Avermaet explained that Polish company CCC were coming on board to save the team, that he was building a squad for the Classics, and that he wanted Van Keirsbulck to be a part of it. The next day Van Keirsbulck sat down with team manager Jim Ochowicz, the day after he verbally agreed to join, and just over a week later pen was put to paper.
"I was surprised, but it was really nice that he wanted me in the team. He wants me as one of his last guys in the finale. Personally, that's better for me. After a while at Quick-Step I was so bored, pulling all day. I like to race and do the finales. The last two years I could do that but it wasn't so easy because I didn't have a team around me. Now I can do it helping Greg.
"I'm super excited to come back to the WorldTour and working for Greg. He's a really good guy. You don't see him as a big leader. Well, he is, but he's just the same as us, you don't see any difference between Greg and a helper, he's so normal, so down to earth. I'd like to prove what I can do for Greg and to show everyone I'm back, and for me that's the most important thing."
The idea of being 'back' is a curious one. In a certain respect, Van Keirsbulck's career never really took off to begin with. Grandson of a former world champion, winner of the junior Paris-Roubaix, and a Quick-Step rider at 19, expectations were foisted upon him. Those expectations were probably always unreasonable, but circumstances have since conspired to put them definitively out of reach.
"I was really young when I turned pro. I was 19. At first everyone was saying 'you're the new Tom Boonen'. It's easy to say that but it's not so easy to do it," he says. "I've had a lot of bad things in my life. That fucked my career a little bit I think, those things."
It can sound trite to describe the new year as a new start, but that's exactly what it is for Van Keirsbulck.
"I'm back here in WorldTour team. It's like a second chance. I try to do everything good now," he says.
"I know in the past I didn't do 100 per cent on everything, but now I'm enjoying it again. That's a big difference. I didn't used to train that much - I didn't like it - but now I enjoy it every day. I can still grow I think, in every detail actually - train harder, eat healthier, all those things. Now I hope everything ends good."
Tom Boonen ended his career in 2017 with four Paris-Roubaix titles, three at the Tour of Flanders, five at E3-Harelbeke, and three at Gent-Wevelgem, along with six Tour de France stages and a world title. It's fairly safe to say the 'next Boonen' ship has sailed, but that's not to say Van Keirsbulck doesn't still have a point to prove.
"I think I have still potential. I can do more," he says confidently.
"I think maybe in the future I can become leader or something. I've won a few races but no big races - I'd like to win a big Classic. I've been cycling for almost 10 years, but I'm still young, I'm only 27. You never know."