Complex sentence: In November 2013, Lewandowski confirmed he will sign a pre-contractual agreement for Borussia Dortmund's rivals Bayern Munich which officially happened on 3 January 2014; signing a five-year contract, joining the team at the start of the 2014--15 season.
Split into simpler sentences: In November 2013, Lewandowski confirmed he will sign a pre-contractual agreement for Borussia Dortmund's rivals Bayern Munich. On 3 January 2014, he signed a five-year contract, joining the team at the start of the 2014--15 season.