On Monday, 25-year-old Tanya Burr announced she was writing a book, and within minutes the news was trending around the world.
In December, Chapman and Burr will celebrate their eighth anniversary together.
This is her first video, from October 2009.
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Burr's videos are predominantly make-up, hair, and fashion tutorials. Five years after uploading that first video, her YouTube channel now has over 2.5 million subscribers.
She also has 1.1 million followers on Twitter, over 500,000 fans on Facebook, and 1.4 million on Instagram.
Her most popular video to date is about the contents of her handbag.
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It has been watched almost 2 million times.
Her fiancé has a similarly impressive following.
Chapman is part of a family of YouTube stars.
And even their mother had her own channel, Modern and Mature, which uploaded 60 videos in a couple of years.
Chapman and Burr are part of an incredibly close-knit group of massively popular UK YouTubers who are all signed to the same talent agency.
The group includes three couples, two housemates, and a young mother. They go on tour together, regularly appear in each other's videos, and at present are some of the most popular entertainment figures in the country.
They are also in the process of making a lot of money.
Alfie Deyes (top left in the picture below) was paid a rumoured £50,000 advance for his debut book, The Pointless Book, the Sunday Times recently claimed.
This is the kind of reaction they receive when they go on tour:
Chapman insists he and Burr didn't get into the YouTube business for the money and career openings.
"Up until recently this has really worried me because I used to think, 'What, why… I’m not going to be relevant in a few months now, I’m not going to be relevant tomorrow – who’s going to keep watching me?'"
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But the 26-year-old said he now believes his audience will follow him wherever he goes.
"As long as I respect them and maintain the relationship that I have with them at the moment, then fingers crossed – this is for the long-haul," he adds.
Chapman admitted though that he wanted to branch out and diversify into TV and radio, and highlighted his modelling and the fact that he's currently writing for a few magazines.
His fiancée has TV plans too, but said that rather than presenting she would love to be on Strictly Come Dancing.
With the mainstream media waking up to the popularity of these young stars in recent weeks, newspapers have been attempting to try to understand their popularity, with mixed results.
On being a role model to millions of impressionable young fans, both Chapman and Burr said it was not something they actively sought but it's a responsibility they are comfortable to shoulder.
Chapman said:
I try and always send out positivity and a good message. Obviously I do a lot of stuff just for fun, that's a bit crazy or whatever, but my goal is to put a smile on people's face.
For a lot of people who are a bit younger, this is a tough time in their life. In today's world it's particularly confusing. I can be the guy who puts the smile on your face or gives you some advice if you need it.
[I'm] not trying to be a role model directly, just the way I conduct myself and lead my life is of that vein – it's all very positive and I like to think just doing what I do in my way is giving a positive effect on people.
Burr added:
It's not a role that I thought would be my role when I started making YouTube videos, at all.
It's just sort of came along but you do have to take responsibility for it because…that's what happens. I have respect my viewers and be a good role model for them, so it is a lot of pressure.
But I don't find it that hard because I'm quite boring – I don't go out, I don't drink loads, I don't do anything that would be really bad. I like baking and fashion and beauty, so I don't think it's that hard for me to be a role model.
Burr said that being engaged and living with another YouTube superstar has both advantages and disadvantages.
She added:
Most office 9–5 jobs, you clock off and you don't care what you did that day and you go for drinks with your friends when you hang out in the evening and have fun.
Whereas our work is constantly on our minds, because it's not just uploading one YouTube a video a week now – there's a lot going on, there's so much press at the moment, and there's books, make-up lines, tons of stuff that we're all working on. It's constantly on your mind.
As well as the regular videos on their main channels, the pair upload daily vlogs showing what they have been up to on any given day. This is Burr's from 2 November.
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It includes a description of what she had for breakfast, and shows her and Sugg at a petrol station, buying underwear, painting their nails, and boiling pasta.
One subject the pair are not willing to share details of with their fans though is their upcoming wedding day.
"People are so invested in our lives that it freaks me out a bit to think of them having any information about the wedding," Burr said.
She said that if they were to publicise their wedding it wouldn't feel like it was theirs any more, but added that fans had been very understanding about them wanting to maintain their privacy.
"They are not strangers, they are our viewers and we interact with them as friends," she said. "They do get excited and would sure be really excited to know the date, or where it is, but I think at the same time they are really understanding, which I really appreciate."