The Audemars Piguet caliber 2225 is a Swiss made automatic movement found in the Royal Oak reference 14790ST. This movement replaced the AP caliber 2125.
The gold on the rotor is 21K. The text reads as follows:
“Thirty-Six / (36) Jewels / Automatic / Adjusted to Heat Cold Isochronism and Five (5) Positions / Audemars Piguet / Swiss / 21C”
Removing the movement from the case:
Removing the 2225 from a vintage Royal Oak requires lifting the movement from the dial side. Carefully remove the screws from the back of the watch, lift the bezel and crystal, then you can access the movement with gasket attached to the movement holder. There is a notch cut out in the case above the stem, not a split stem.
On the watch this movement was found in, the reference part numbers signed on the gasket are: EP-925034 (top number) / 193.014 (bottom number).