Ceballos and Saliba join Unai at the Emirates
Arsenal have announced the signing of William Saliba from St Etienne on a long-term contract.
The 18-year-old defender will spend next season on loan at the Ligue 1 club before linking up with the Gunners next summer.
Saliba was the second deal confirmed in the space of two hours by the Premier League club after the capture of Real Madrid midfielder Dani Ceballos on a season-long loan.
Arsenal are believed to have been interested in the teenager for some time and but finally landed their man for a fee reported to be in the region of £27million.
"Highly-rated French defender William Saliba is joining us on a long-term contract," the club announced.
"The much sought after centre-half will spend a season back on loan at St Etienne before joining our squad next summer."
Head coach Unai Emery added: "We're delighted William is joining us. Many teams wanted him but he decided he wanted to come to us and be part of our future.
"He will stay in France next season for more experience and then we look forward to him joining our group."
Ceballos revealed the prospect of working under Emery was the "turning point" in his decision to join on a season-long loan from Real Madrid. The 22-year-old Spain international is highly regarded at the Bernabeu and made 23 La Liga appearances throughout the 2018/19 campaign.
But Ceballos, who has six senior caps and also helped Spain's Under-21s to Euro 2019 success this summer, will now spend a year in north London after agreeing to a temporary switch to the Emirates Stadium.
Other options - including from rival Premier League clubs - are believed to have been on the table but Ceballos insists the lure of playing for Emery made up his mind.
"The coach was the turning point in terms of me joining this massive club," he said. "He's a Spanish coach and he knows me from my time at other clubs. I'm really happy to be able to help Arsenal achieve our objectives.
"I knew I had the confidence of the coach, which was very important for me."