Romero arrived at Getafe on loan last winter as an emergency fix and swiftly established himself as the marshal of José Bordalás's back line.
According to the club's official statement, the two sides have now reached a full agreement over a permanent transfer for the 26-year-old, worth around €5m and running on a contract until 2030, securing what Getafe view as a cornerstone piece for their defensive setup as they prepare for a Conference League campaign.
During his loan spell from January through the end of last season, Romero settled seamlessly into Spain's notoriously demanding top flight. He featured in 15 official matches and even opened his goalscoring account for the club, though it was his composure and reading of the game that most impressed the coaching staff and ultimately convinced the sporting department to make the deal permanent.
The move comes as Getafe's hierarchy work to freshen up the squad more broadly, with club president Ángel Torres having signalled that as many as 14 new faces could arrive before the summer window closes.
Romero came through the Godoy Cruz academy and has since built a well-travelled career, with spells at Villa Dálmine, LDU Quito, Estudiantes de La Plata and, most recently, Club Brugge before his switch to Spain. Getafe pointed to three qualities in particular from his loan stint: an unshakeable defensive solidity, dominance in the air, and a rapid adaptation to life at the club.
The move means Bordalás retains a defender who already knows the club's workings and demands no adjustment period.
"Getafe CF add a player who already knows the club and will bring security and competitiveness to the back line," read the club's official statement, which closed with an enthusiastic message: "Welcome back, Zaid!"
The deal rounds off what Getafe consider a shrewd piece of business, locking down the present and future of their defence with a player who has already shown he feels part of the project and is ready to perform at the highest level.
It also arrives with the Coliseum itself in transition, as the club presses ahead with a major stadium redevelopment that will reduce capacity for large parts of next season.