Singer visited the Mayan archaeological site in Tulum this week
Bieber's getting in the Christmas spirit in close-run chart race
Singer has expanded his fanbase by 10% in the past two years
Both acts join Adele on the line-up
Dennis Graham started his career as a drummer in Memphis in 1962
Extra dates in Birmingham and Manchester also added
2016 arena tour is extended
Bieber could be disqualified following campaign by Australian gambling company
Bieber will bring new album 'Purpose' to the UK in October 2016
The pop star recently replaced himself at Number One in the UK Singles Chart, matching a record only held by The Beatles and Elvis