Following weeks of transfer speculation, the Gunners completed a £75M transfer swoop to sign Guimaraes, as the Magpies saw another big name head for the S. James' Park exit door.
The Brazil international scored 31 goals in 195 Newcastle appearances across five seasons on Tyneside, but he's ready for a new challenge, and pledged to add something different to Mikel Arteta's squad.
"I'm so excited to join. I will give you my best, I promise. I'm your warrior, I'll never give up. Hopefully we can create many, many good memories together."
Alongside his message to the Arsenal fans, the former Lyon playmaker also revealed he'd received a message of his own from Declan Rice.
The pair have clashed several times in recent years, but that looks to behind them now, as Arteta has the two stars manning his engine room.
"Rice sent me a message: 'Come here and please no more fights, now we're friends,'" Guimaraes said after completing his switch to the Emirates.
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"I was happy he messaged me, but the midfield we have here, in my point of view, is one of the best in Europe.
"Everyone is an amazing player, I'm so excited to start. I know the players very, very well, but we have an amazing midfield."