Staying at Juan Carlos place was a great experience.
His place is located right in the middle of Sevilla's center (next to Alfalfa square), with a lot of markets, bakeries and other stores nearby. His appartment is big enough for 4-5 people, it has a very nice kitchen fully equipped (dish washing machine + clothes washing machine, coffee machine, oven, etc.), a nice bathroom with hair dryer (and Juan left us some shampoo, hair conditioner and soap), two bedrooms (one with a double bed and another one with two single beds) and a cozy living room.
The only thing we missed was wi-fi.
Also, if you go to Sevilla by car, be warned that it is a very difficult city to park for free. Despite that, there's some parking spaces next to the flat, which is quite useful.
Last but not least, if you're worried about the environment, let me tell you that at Juan Carlos place you'll even find different baskets to separate garbage. It is that sweet ;)
I also have to say a word about Juan Carlos friend, Manuel, which was kind enough to stay awake until 3 am, as we had some serious mechanical problems during our road trip and arrived pretty late.

All in all, I strongly recommend this place to stay. If I ever come back to Sevilla - which will most certainly happen - I will contact Juan Carlos in the first place.