Arsenal confirmed the signing of David Luiz on Thursday, three hours after the transfer window closed on deadline day.
The transfer window closed at 5pm on Thursday.
The reason Arsenal were able to sign the player late, was because they filled a deadline day deal sheet, giving them until 7pm to finalise the deal.
A total of six deal sheets were submitted ahead of the 5pm deadline, the Premier League confirmed via their official Twitter handle.
The Gunners agreed on a £8million transfer fee with Chelsea for the centre-back.
Luiz will now be reunited with manager, Unai Emery, after working together at Paris Saint-Germain.