what is this seed, is it a weed or flower?

looks like Honesty, though not the same as some we had, so maybe there are several different varieties. I'm unsure about the weed/not weed thing - maybe the jury is out on that, a bit like forget-me-nots which personally I love.
They're definitely not the most annoying kind of "weed" ie impossible to get rid of in case you don't like it!

I thought it was honesty

I was thinking honesty too initially but the seeds look concentrated in the middle and that doesn't seem right.

Does look like honesty.....

No - it's defo NOT honesty!! Sorry, i don't know what it is, but it's not honesty!! How tall is it?

i agree with sid. honesty seeds are arranged singularly through out the papery pod and they are not usually this brown either.
as sid asks could we please have more details. by the way what plants did you have in the bed?

Its called Field Pennycress, genus Thlaspi.