Robbie Williams has opened up about his struggles with fame.

The 51-year-old singer took to Instagram to share a lengthy post where he explained how fans asking for selfies can cause him discomfort and panic and he shared some examples from a recent flight he took in America.

Robbie wrote: "I'm sat on a domestic flight, going across America.

"I've had three interactions so far with fellow passengers. One of them handed me a lovely note -kind words about my documentary - and then asked for a photo.

"I wrote a note back. I explained I'd been up since 4:30 a.m., had two hours' sleep, and wrangled four kids through the airport. I've got bags under my eyes and I'm dealing with anxiety. I explained that if they came and took a photo with me, my anxiety would spike - because then the whole cabin would start wondering who I am. And I'm not famous here.

"That kind of attention would only pile more anxiety on top of my already-thriving 'being outside' unease. I didn't say no I wrote back, offered the letter, and said: 'Lots of people have photos with me, but no one's got one of these.'

"Then a lovely steward came down and said there was a man at the back of the plane who was a big fan of 'Rock DJ' and wondered if he could come take a photo. I wrote a similar note on the back of my plane ticket and said that when we land, I'll be trying to shepherd four children. Again, I didn't say no. I just hoped the note might be enough.

"As I was writing that one, another passenger walked up and just asked outright for a photo. I obliged.

"These days, I see it as being of service. If it makes someone happy and I can then I'll do my best to facilitate that happiness. I didn't always see it that way. But I do now. Mostly.

"Still... I think there needs to be a caveat. So let me try to explain. This is dodgy terrain for a famous person to give context around. Anything short of: 'Of course, it's my duty and the right thing to do' ...is risky.

"There's a kind of unspoken law: as a celebrity, you should be accessible 24/7. Greet all strangers like you're the mayor of the best town anyone's ever visited. Make sure their wishes are met, whatever they are.

"Otherwise you're a ****. There's no in-between. I've seen the argument: These people put you where you are should." so you

"But that thinking's off. I reckon over 50 per cent - probably much more couldn't name one of my albums, let alone say they've bought a ticket to a show. They're no more fans of me than they are of the Leaning Tower of Pisa or Big Ben. They're fans of fame ..."

Robbie went on to explain the reasons he might not want to take a picture, saying: "Maybe I'm on the phone with my Mum, talking around her dementia.

"Maybe I'm thinking about my Dad's Parkinson's. Maybe I'm just... sad. Is it okay to sit in that sadness without having to perform? I'm not saying don't ask. You can. And I'm not saying all celebrities are saints. We're the same ratio of good and bad as wherever you work. Look around you - What I am saying is: let people be people. Humans, struggling - like we all are in one way or another. Allow people the dignity of their privacy, their wants, their needs. Because most of us are just trying to protect ourselves - mentally, physically, or both. Just like you."

Robbie received support on the post from his fellow celebrities, with Kris Jenner commenting: "Wow so beautifully said and I really understand this… thanks for being so brave and vulnerable and for explaining this so thoughtfully and so well…sending love. God Bless."

Adam Lambert wrote: "this resonates. I think it's helpful to explain it because it's hard for the public to understand what it's like from the opposite perspective. Thank u for this!" and Aimee Lou Wood said: "This is so perfectly put. Planes are particularly intense because you're trapped in the sky."

And, Paris Hilton said: "This made me cry.. love you bro, thank you for being vulnerable and saying how you feel."