The 19-year-old YouTubers, better known as the Dolan Twins, each shared photos of their father on Instagram and revealed that he had passed away.
"You will forever be my best friend," Grayson wrote in a post. "You are responsible for making me the person that I am so proud to be today. All of the lessons that you’ve taught me have stuck with me and I will use them moving onward for the rest of my life. You are and forever will be my favorite person that I will ever know."
Sean Dolan, a school principal who lived in New Jersey, was diagnosed with cancer in 2016.
"You never let it fade you," Grayson wrote. "Not once did I hear you complain about your condition."
Last week, the family learned he had less than a week to live, but he lived a week and a day. "That alone shows the type of man you were, a fighter," Grayson wrote.
"You're the man. I love you Dad."
Ethan echoed his brother as he shared the news with his own Instagram fans.
"Dad, you were so much more to me than just my Dad," he wrote. "Although we were only granted 19 years here together it feels like we’ve spent a million lifetimes together. You are such a strong soul and you’ve made such a strong impact on more people than you would believe."
He continued, "When you were very sick you told us, 'This disease may get my body, but not my mind and not my heart. As long as my heart is beating I will still be fighting.' That is exactly what you did Dad. ... Cancer may have taken your life but with the strength and dignity you showed, and the inspiration you left us with, you won the battle Dad."
The brothers also updated their fans on Twitter, and said they'd be taking some time off to be with their family.
They have shared details of their father's cancer battle with their fans in the past. They opened up about his diagnosis in a 2016 video, "You Are Not Alone."
“Recently, our dad was diagnosed with cancer," Grayson said in the video. "And you know, news was just thrown in our face, and we really didn’t know how to act at first. I never thought that someone close to me would, you know, get cancer, or have something as serious as this happen to them. But it did."
He continued, “I just try to appreciate every moment that I’m with my dad and being with my family and being with my friends. It also made my really appreciate my health and realize how important it is to not take things like that for granted.”
His brother added, "Just take a deep breath. Go through that big stack of paper of terrible news and find the positives in it."
The twins, who are from New Jersey, started posting comedy videos to Vine in 2013.
They now have nearly nine million YouTube subscribers on their channel, Dolan Twins, and a combined 17.5 million followers on Instagram.