The club announced the signing of Cesar Azpilicueta on 24 August 2012.
The 22-year-old right-back, who represented Spain at the London Olympics, arrived at Stamford Bridge following a two-year spell in France's Ligue 1 with Marseille.
He joined fellow countrymen Juan Mata, Oriol Romeu and Fernando Torres at the club.
Cesar made his debut for the club in the 6-0 win over Wolverhampton Wanderers at Stamford Bridge in the Capital One Cup, playing the full 90 minutes.
His first Premier League appearance came shortly after when he replaced Branislav Ivanovic midway through the second half of a 4-1 win against Norwich City, while his first league start came in the 1-1 draw with Swansea at the Liberty Stadium.
As the season progressed, the young defender went from strength to strength and established himself as a regular in the side at right-back, with Ivanovic playing more often than not in the centre of defence.
Such was Azpilicueta's influence that, as the games piled up, and Rafael Benitez continued to rotate the side, he was one of the few players seldom rested.
He played an integral role as the Blues secured a third-place Premier League finish and completed the full 90 minutes in the Europa League final win over Benfica in Amsterdam, bringing his first season at the club to a triumphant finish.
The Spaniard then scored his first Chelsea goal from the penalty spot in a 4-3 friendly defeat to Manchester City in the US, and notched his first competitive goal for the Blues in the 2-0 win against Arsenal the following season.
Born on 28 August 1989 in Pamplona, Navarre, he began his career at the academy of his hometown club, Osasuna.
Having started out as an attacking midfielder, Azpilicueta is comfortable in possession with a good range of passing.
Having come through the ranks at Osasuna, Azpilicueta was handed his La Liga debut on 8 April 2007 against Real Madrid at the Bernabeu.
The following season, with Osasuna depleted by injuries, the youngster featured regularly and cemented his place in the team at right-back with a string of impressive displays, while the 2008/09 campaign saw him miss only two games.
In June 2010, Azpilicueta made the switch from Spain to France, signing a four-year deal with Marseille. The youngster, however, endured a difficult opening to his career at the club suffering a knee injury which ruled him out for his first season.
Following the disappointment of the previous campaign, the 2011/12 season - with both the European Championships and Olympics on the horizon - was always going to be a big one for the young Spaniard. He flourished, performing consistently well and catching the eye as Marseille reached the Champions League quarter-finals, eventually eliminated by beaten finalists Bayern Munich.
At international level, he has represented Spain since earning a call-up to the Under 16s in 2005, and was part of the Under 19 side which won the European Championships back in 2007, as well as the Under 21s who tasted success in the same competition in 2011.
After impressing during a sustained run in the side, Azpilicueta earned his first senior call-up for Spain for the friendly against Uruguay in February, and played the full 90 minutes in a 3-1 win. He also featured for his national side at the 2013 Confederations Cup in Brazil, playing the full 90 minutes in the emphatic win against Tahiti and coming up at half-time in the final defeat to the host nation.