Son of former footballer Marcos Alonso Peña (aka Marcos Alonso).
Grandson of former footballer Marcos Alonso Imaz (aka Marquitos).
Had a drunk-driving accident causing the death of a young woman in Madrid. (May 3, 2011)
Won the Premier League (2017), the FA Cup (2018), the UEFA Europa League (2019), the UEFA Champions League (2021), the UEFA Super Cup (2021), the FIFA Club World Cup (2021) and the EFL Cup (2022) with Chelsea F.C..