 Complete the following phrase:  Bertrand began his youth career at Gillingham, before signing for Chelsea in July 2005. He graduated from Chelseas youth system and was sent on loan to various clubs between 2006 and 2010. He made his full debut for Chelsea on in April 2011, six years after joining them, in a fixture against Birmingham City. In the 201112 season, Bertrand signed a new four-year contract with Chelsea and was made understudy to Ashley Cole. In May 2012, Bertrand became the first player to make his Champions League debut in the 