Sir Paul McCartney
Sir Paul McCartney isn't too rich or famous to ride public transport Getty

Sir Paul McCartney may be worth an estimated $660m (£508m) but the Beatles legend is not too proud to use public transport. A fan spotted the Ticket To Ride singer riding a train from London, proving McCartney might just be one of the most humble superstars around.

The photo, which was shared on 29 June, shows McCartney, 75, sitting alone in First Class without an entourage or security and reading a set of papers. The British singer is bundled up against the chilly weather in a thick black coat and a scarf and seems to be unaware that a fellow passenger has spotted him and is taking a sneaky picture.

According to the Mail Online, McCartney was travelling from King's Cross in London to Hastings. An onlooker claims that at one point, the Hey Jude hitmaker was "looking at his old school Nokia" mobile phone.

Another city-worker who also spotted the music icon, added: "He was on his own without any bodyguards or staff. Only a few people stopped to say hello and that it was nice to see him.

"He didn't want photos but he was very polite and happy to chat, talking about a new album he has coming out. It was unusual seeing such a massive music star just sat on his own."

Clearly comfortable with making the journey on his own without bodyguards, it is likely that McCartney is a regular user of public transport. Longtime fans of McCartney will remember the music video for his 1986 solo single Press, which features the musician riding the London Underground and getting up to mischief with other commuters.

McCartney joins a fleet of other celebrities who have used public transport in recent years. Musicians Chris Martin, Rod Stewart, Jay Z and Rihanna are among those spotted on the Tube while actors Eddie Redmayne, Kim Cattrall and Richard Madden have also been caught in the act.

Beatles fans celebrated the 50th anniversary of their pioneering album, Sgt Pepper's Lonely Hearts Club Band, earlier in June but McCartney is looking to the future. The musician is busy recording new music with his former bandmate Ringo Starr and Eagles singer Joe Walsh. McCartney has also announced his One On One Tour will head Down Under, performing five shows in Australia for the first time in 24 years.

Watch Paul McCartney ride the Tube in his Press music video: