They are two of the most popular YouTube stars out there, with more than six million subscribers on Facebook.
But The Dolan Twins' planned meet-up in London on Sunday did not go as expected, after the duo discovered a memorial for Remembrance Day was being held in Hyde Park.
Taking to Twitter, Grayson, 17, explained he had 'no idea' that the memorial was taking place, adding that he felt 'horrible'.
He and brother Ethan announced that they would have to cancel the meet-up, to the huge disappointment of their followers.
In fact, hundreds of young fans had already turned up in a bid catch a glimpse of their idols, with footage showing them running about in Hyde Park.
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The Dolan Twins were forced to cancel a meet-up in Hyde Park at the last minute after discovering a Remembrance Day memorial was taking place
Less than half an hour before the planned event, Grayson, 17, said he had 'no idea' that the memorial was taking place
He said that he and his brother Ethan would not be going ahead with the event, explaining that they didn't want to be 'disrespectful'
The brothers, both from New Jersey, had announced the mass meet and greet on Saturday, with Grayson tweeting: 'LONDON! MEET UP AT HYDE PARK TOMORROW AT 12:30 PM! I wanna see you there!!'
The meet-up was still due to get ahead at 10.30am on Sunday, when he posted: 'If you are going to the meet up today PLEASE stay calm. I want this to work so we can all have a good time!
'If Ethan and I can’t take a picture with every person individually we at least want to see you all. But stay calm! No pushing others please. Spread the word'.
Less than half an hour before the event was due to take place, Grayson announced that they would not be able to go to Hyde Park for the meet-up, writing on Twitter 'I don’t think the meet up is going to work today guys.'
However, hundreds of young fans had already turned out at Hyde Park ahead of the meet-up
Taking to Twitter, one fan wrote 'There's so many people' while another added 'this is mad'
He explained: 'Guys I had no idea there was a memorial in Hyde park today for remembrance day. It’s more important to pay respect than anything right now. I feel horrible.'
Grayson is believed to have been referring to the service that takes part at the Royal Artillery memorial at Hyde Corner, which is situated just outside the park.
Announcing the event was cancelled, he added: 'Ethan and I are really sorry. We can’t go to Hyde park but we’re trying to figure something out.
'We want to see you guys but we don’t want to be disrespectful and most of all we want everyone to be safe.'
The Dolan Twins, who are from New Jersey, were in London for the MTV Europe Music Awards (pictured)
Some people took to Twitter to criticise fans who failed to leave Hyde Park after the event was called off
However, photographs and video footage posted on Twitter showed that hundreds of fans had already turned up in Hyde Park in anticipation of the event.
One fan tweeted 'THERE'S SO MANY PEOPLE', while another added: 'OH MY GOD.this is mad'.
Meanwhile, others criticised the fans for remaining in Hyde Park despite the event being cancelled.
One wrote: 'Can't fans leave Hyde park already? This is what the twins were worrying about: safety of others, the chanting, the flood of fans'.
Another added: 'Please go home everyone #Dolandtwinshydepark we let as soon as they cancelled.'