Willian and David Luiz go way back.
The duo first met when they were eight years old, playing football in Brazil, and have since gone on to play together for Chelsea and their national team.
And Willian says they're both delighted to have reunited in north London.
"He's very happy," our forward told Arsenal Digital. "We played together in the national team, we played together at Chelsea, and now at Arsenal again. I think we can do great things together, I hope so, but I'm very happy to be with him again.
"He said, 'Come to Arsenal, come to Arsenal, I want you to come!