At age eight, the 27-year-old made his debut for his hometown club Barcelona before switching to Arsenal at age 16.
Bellerin represented Arsenal in 183 Premier League contests and won three FA Cups with the team. While on loan to Real Betis last year, he won the Copa del Rey.
He has four caps for Spain.
Sergino Dest, an American who Barcelona loaned to AC Milan on Thursday with the option to purchase for 20 million euros, is replaced by Bellerin.
Barcelona allegedly agreed to sell Gabon striker Pierre-Emerick Aubameyang to Chelsea for roughly £7.5 million (8.7 million euros) as defender Marcos Alonso, a product of the Real Madrid youth system, went the other way during a hectic summer transfer window.
Earlier in the transfer window, Barcelona purchased Raphinha, Robert Lewandowski, and Jules Kounde in addition to signing free agents Franck Kessie and Andreas Christensen.
the website jestysports.com
Journalist: Seth Pablo