ABBA's Björn Ulvaeus surprises fans by busking in a train station

ABBA fans got the surprise of their life recently when they spotted none other than Björn Ulvaeus busking in a metro station in Stockholm.

Armed with a guitar, a begging bowl and a stack of CDs, commuters were stunned to see the chart-topping Swede trying to make some extra cash.

However, it turns out the 76-year-old - who was dressed up as a cowboy - was putting on the performance for a very special reason.

The musician wanted to surprise one of his good friends, Tomas Ledin, for his 70th birthday.

For a fun birthday video, Ulvaeus re-wrote one of his old Swedish songs from the 1970s called 'Hej Gamle Man' and turned it into a country track called 'Hey Grand Ol’ Man.'

In the footage, Ulvaeus can also be seen doing a spot of line dancing too.