Marca reports The Gunners were heavily linked with Partey all summer but went for broke in the very early hours of deadline day.
The Gunners, though, had other ideas, and decided this would be the right time to get the ball in motion and phoned the Ghanaian's representatives at 2am, prompting 'everything to change'.
Partey allegedly learned of Arsenal's intentions on Monday morning, with Marca reporting that the midfielder and agent 'could not have imagined' that he had already played his final game for the La Liga club.
The midfielder is then said to have been 'put on the spot' and made to make a decision before Arsenal later triggered his £52.5million release clause.
All in all the Gunners splashed out £110m on Partey, agreeing to pay him £260,000-a-week for four years and handing him a £2.5m signing-on fee.
Partey's agent also made 10 per cent commission from the deal.