Chelsea have announced the signing of striker Romelu Lukaku from Inter Milan on a five-year deal.The Belgium international returns to Stamford Bridge having previously played for the Blues between 2011 and 2014.Head coach Thomas Tuchel had been keen to bolster his striking options on the eve of the new season as the German eyes a tilt at the Premier League title in his first full season in charge, having won the Champions League last campaign.