Wow, I had the exact same situation. My bro being my knight and regent came along for the melee and appeared in the very first event.
Same here, except it was my spouse. Started a quick game as Mathilda just to check out some of the new features. The Kaizer almost immediately sponsors a Grand Tournament. Great! My new husband is my presumptive regent. That's fine, he's competent and likes me. The game tells me I'm not going to make it to the tourney in time. Uh oh. Oh well, I'll try anyway, just to check out the travel mechanics. Hey, there's a spot to hire a Caraven Master. I appoint an Average one and suddenly I'm going to make it in time. Awesome! But there's some severe danger spots. Can't figure out exactly where they are, but I guess it's from crossing the Alps. Hire some mountain folks and some regular guards and ta da! The road ahead is clear.
All awesome stuff so far! I bid hubbie good bye, ask him not to ruin the treasury while I'm gone and ... discover he's travelling with me on the first event. Umm, how can you be Regent when I can't be Duchess and we're travelling in the exact same entourage??? Ugh.
PS that first event was a line of ants. Turns out my husband is a superstitious fellow, so I agree to walk around the ants ... which takes 5 days ?! What's with these ants??
Second event is some big guy in the road, challenging me to a fight. He makes a point of telling me that he has defeated "many women" in fights and he'll beat me, too. Seiously, dude? That's what you're bragging about. I don't like this bully of women so I tell my whole entourage to rush him and we just trample over him. Get this, though, supposedly this causes a 30 day delay in our travel ?! I think that's a notification error, though, because after trampling him (hubbie got injured when we rushed him by the way; serves him right for not staying home to be regent like he's supposed to) we make it to the tourney a couple of days early (the third event allowed me to gain 7 days by translating for our caravan master, offsetting the ant delay).
Anyway, dev team: is it that difficult to set an "is_regent" check when figuring out who can join our entourage to keep your Regent from coming with you? I mean, maybe it is difficult, this is legitimately a question. But if you can prevent your Regent from travelling with you, for heaven's sake please immediately do so. It's just weird right now.