Neutered rabbit becoming agressive?

We have a 1 Year old continental giant rabbit (Blue) that we adopted (with his brother) from 2 months old. I love rabbits and have owned 4 altogether. I know everything about their needs and behaviours and want to work with animals in the future. This is why it is so upsetting so see my rabbit becoming agressive. Although male and male rabbits commonly don't get along, we decided to try and keep them together seeing as they were brothers and were still young. At 3 months we got them neutered and it was at about 6 months that they started fighting eachother. After several months of trying we knew this bond wasn't going to work and did not have adequate space to keep them both separate and happy. Regretfully we therefore decided to give one to my college as they specialise in animal management (course I am taking) and this way I could see him everyday. He (Kumo) was successfully bonded to another female continental giant. We decided to keep Blue as we knew he was less likely to bond; he always initiated the fights and was very territorial about his house (8x6 shed). His brother Kumo has the raised by us exactly the same yet is very sweet and loves to be stroked. Blue on the other hand has gotten to he point where he boxes at you when you try and stroke him, he grunts whenever I come near him and will lunge to bite if do not give him his food straight away and/ or try and stroke his head (no matter how slowly I move my hand). For a few months I've tried various things such as feeding him when he comes near me and then stroking him (which he accepts) and sitting in his accommodation with him so he knows I'm not a threat. We were originally thinking about bonding him with a female but considering how territorial he is, we not longer think this would be a very good idea. He gets everything he requires, gets at least 5 hours exercise in a large pen each day; he binkys all he time and genuinely seems happy except when we try to come near him. I don't understand what I've done wrong and this is really upsetting for me. Is this just part of his characteristics? Is there anything anyone recommends me trying to help him trust people more? As long as he's happy I don't mind not being able to stroke him and no matter what will we keep him forever. I'm just confused as to why he's become this way? Sorry for such a long paragraph, any answer will be appreciated

Unfortunately, sometimes a rabbit's behavior takes a turn for the worse after being neutered/spayed. Others have come here with the same issue...it doesn't happen a lot, but it does happen. You can try some discipline techniques to see if it will help because he does need to know that you're the alpha, not him. It also sounds like he was pretty territorial prior to the neuter, and for which neutering may or may not help.

I have only had two males that have not been aggressive to each other. All the others are even with being neutered. I even had a bonded pair male female that suddenly became unboned.
Being brothers they had more chance but I think it is just them being mature rather than the neutering that caused the problem. You be able to work with them and get them to basically get along.
They sound like they have territorial issues or something in the environment that is causing the aggression.
Others may have better advice.

Unfortunately it's almost impossible to tell why he may be this way, especially if you're catering to all his needs. It may simply be his nature. As mentioned you had him neutered before he matured, so his true personality hadn't come through yet. It's possible that he's simply just a very territorial rabbit, some are more than others and I doubt it's due to anything you've done wrong.

Thanks for replying everyone! All very helpful I will let him know I'm in charge and continue to keep trying with the socialisation techniques.