Dougie Poynter feels "honoured" that McFly are a "nostalgic" act.
The 32-year-old bassist and his bandmates - Tom Fletcher, Danny Jones and Harry Judd - reunited in 2019 after a three-year break, and the group are delighted they have managed to maintain a huge fanbase.
Dougie said: "[The original fans have stuck with us] and some of them have gone on and multiplied and brought their kids along.
"I'm really honoured to be one of these nostalgic acts.
"I'm pretty stoked that I'm 32 and still get to play The O2.
"Our manager always said when we had our first number ones, 'Celebrate now but celebrate when you've been a band for 10 years.'
"It's been 16 years."
Dougie admitted he and his bandmates were always baffled by the level of devotion they inspired.
Asked their craziest fan moment, he told new! magazine: "Touring South America. They'd chase us in our cars and we'd be like, 'How can you be passionate about us? We're a bunch of nerds."
The quartet are very close but still have arguments, though Dougie sees them as positive.
He said: "We all get on. We bicker every now and then, but like a family would.
"It's usually about the set-lists. The rad thing is, it's not a selfish thing, it's about what we think other people want. It's not full on arguments."
Although the 'Please, Please' hitmakers don't go "wild" on tour, they can get "stupid" when they're all together, though they try to look after themselves too.
Dougie said: "It's not really wild, but it's stupid.
"We're pretty hyperactive and just disgusting boys.
"But we love doing what we do so much that we et the right amount of sleep so the show is good. We keep ourselves healthy and fit."