Bertos was born in Wellington, to a Greek father and New Zealand mother. He attended Holy Cross primary school (1987–1994) and Wellington College (1995–1999) where he played for the school's 1st XI.
Bertos played for Wellington Olympic in the New Zealand domestic league between 1997 and 2000.
Bertos started his career in England, playing in Barnsley's youth system. He made his debut for the Barnsley reserve team against Rotherham United in October 2000. and his first-team debut for Barnsley in a 0–4 defeat to Preston North End on 16 April 2001. Bertos signed a professional contract for the club a day later. He picked up a knee injury whilst playing in Tenerife, the results of which required a second opinion. These results were delayed,<ref name="Bertos... Read More