Michael Ballack's son Emilio has died aged 18, the ex-Germany international's former club Chelsea have confirmed.
Portuguese television station TVI reported that Emilio had died as a result of a quad bike accident.
Chelsea offered their condolonces to Ballack and his family by releasing a statement on Twitter.
"Everybody associated with Chelsea Football Club is shocked and saddened to learn of the death of Emilio Ballack at the terribly young age of 18," Chelsea announced in a statement .
"All our thoughts are with his father Michael and his family at this sad time."
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Ballack came to prominence as a member of Kaiserslautern's surprise Bundesliga-winning squad in 1997-98, before he sealed a move to Bayer Leverkusen in 1999.
A three-year spell with the club saw him establish himself as a key mainstay of the Germany national team, including a silver-medal finish at the South Korea/Japan 2002 World Cup, before he moved on to Bayern Munich.
There, Ballack enjoyed further success, including a further hat-trick of Bundesliga crowns and a third-place finish on home soil at the 2006 World Cup, after which he moved to the Premier League.
With Chelsea, he completed a clean sweep of domestic honours across a four-year stay, and came within a penalty shootout of a Champions League crown, edged out by Manchester United in 2008.
He moved back to Leverkusen in 2010, where he finished his career, hanging up his boots in 2012 after turning down moves to MLS and the A-League.
Ballack has two other children, Louis and Jordi.
