Aguero was in Manchester yesterday for talks at Etihad stadium.
Aguero flew in from Buenos Aires, via Heathrow, early in the morning and went straight to a private Manchester hospital to undergo his medical.
He then had a brief stop at City's stadium before deciding lunch was the next most important thing on the agenda and so disappeared for a few hours before returning to the ground in the early evening.
After holding discussions with City officials, the son-in-law of Argentina icon Diego Maradona happily signed autographs for the growing crowd of fans who had gathered to see their new hero.
"I'm already a City player. Happy to be in this club & this city," he wrote on Twitter afterwards.
"Thanks everyone for the welcome and reception."