I think he might be ready to start transitioning to 1 nap a day.
You can use Alex's suggestion and keep a late morning nap instead of an early pm nap, or you can start pushing the am nap back to around noonish and keep it there for awhile until you feel he's capable of staying up until 1 pm or so. The afternoon nap, as it is, can either be eliminated or shortened to be only 45 mins (a cat nap).
OR, you could start shortening the am nap to no more than 45-1 hr, and try for a nice long afternoon nap, eventually eliminating the morning nap.
Basically you have a few options here. Just do what you feel is the best course to make the transition. It doesn't have to happen in 1 week. It doesn't have to take a month. It can take 2-3 months or more if you're comfortable with it, based on his reaction to the change.
There is a thread somewhere recent in the nap forum with a long discussion of transitioning to 1 nap, and there is a thread at the top of the nap forum that discusses it.
Good luck!
*HUGS*
Sonya =P