The Take That star took to Instagram on Thursday night to open up about a recent encounter he had with a fan.

"I'm sat on a domestic flight, going across America. I've had three interactions so far with fellow passengers," he wrote in the candid post. "One of them handed me a lovely note - kind words about my documentary - and then asked for a photo."

Robbie then explained that he declined the fan's request because he was "dealing with anxiety".

"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," the Angels singer wrote. "I've got bags under my eyes and I'm dealing with anxiety."

He continued, "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."

Robbie went on to admit that this kind of attention would "only pile more anxiety" on him, noting that he already feels uncomfortable "being outside".

The Rule the World singer then revealed he had turned down a photo request from a second fan, explaining he had written a "similar note" saying he was busy with his children.

The hitmaker has four children, Teddy, Charlie, Coco and Beau, with his wife Ayda Field.

Speaking about posing for pictures with fans, Robbie said, "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."

However, the singer also noted that social interactions often make him feel uncomfortable.

"Every interaction - with strangers or even people I know well - fills me with discomfort," he admitted. "I mask it well. But social interactions still frighten me."