Complex sentence: Frattini was a candidate to succeed to Anders Fogh Rasmussen for the post of NATO's secretary general in October 2014, but the post has been given at the beginning of the year to Jens Stoltenberg.
Split into simpler sentences: Frattini was a candidate for the post of NATO's secretary general, currently held by Anders Fogh Rasmussen. He was a candidate to replace him in October 2014, but the post has been given at the beginning of the year to Jens Stoltenberg.