A rep for the star confirmed that Harry's stepdad passed away earlier this week.
"Harry’s stepfather, Robin Twist, sadly passed away this week after a long battle with cancer. The family asks for privacy at this time," the rep said.
In 2013, the One Direction singer's mom, Anne Twist, married Robin. The "Sign of the Times" singer was the best man at their wedding. His older sister, Gemma Styles, was the maid of honor at their nuptials as well.
When talking about the wedding, Hazza said that giving the best man speech was one of the most intense experiences of his life.
"I practiced on my own for days beforehand, on the sofa reciting it to myself. I tried to make it have a bit of everything. When everyone thought it was going to be really emotional, I pulled the rug out from under everyone's feet and injected a bit of humour. It seemed to go well," he said at the time.
Harry and Gemma were extremely close to Robin in the years after his parents' divorce. Robin also has children from a previous marriage, Mike Twist and Amy Twist.
Before Harry joined 1D and started his journey on X Factor, Robin was right there with him. When Hazza was 16 years old, he auditioned for the reality competition show — and Robin, along with the rest of Harry's family, were cheering him on backstage.
Harry's 1D bandmate Liam Payne took to Instagram to share a sweet photo of Robin and Anne, along with a heartfelt message.
"Harry my heart really goes out to you such an extremely sad day for us all who knew Robin. What a kind, gentle and beautiful soul, a true rarity to find in today's world. Sometimes they really do take the best of us far too soon. X," Liam wrote.
Niall Horan also shared the same photo of the couple on Instagram and wrote a truly touching message in the caption to his brother Harry too.
"Very sad to hear about the loss of Robin . For those who had the pleasure of knowing Robin will know that he was the nicest , kindest, most generous , hilariously funny guy you'll have met . He always had a smile on his face even when he was battling the terrible illness . Love ya H . Please give your mum and the rest of the family a massive hug from my family," Niall wrote.
Louis Tomlinson took to Twitter to share his condolences to Harry and his family too.
Devastated to hear the news about Robin . He was the such a lovely kind and funny guy. Sending all my love to the whole family.— Louis Tomlinson (@Louis_Tomlinson) June 22, 2017
You'll be missed mate :(— Louis Tomlinson (@Louis_Tomlinson) June 22, 2017
The 1D fam is for life, there for each other, no matter what. Directioners have expressed an outpouring of support for Harry and his family too, using the hashtag #RIPRobin on Twitter, to honor Robin as a true member of the 1D family, bringing a "happy, smiley, cheerful, wonderful" presence to the world.
Our thoughts our with Harry, Anne, and the entire Twist family.