Just realised I never actually uploaded the flag to go with my Iberian coat of arms!
So here is my flag for a united Iberian state, featuring the Cross of St James. I chose to use the Cross of Santiago, as it is sometimes called, over an amalgamation of arms or colours and the such because no matter how many times I re-jigged it, I thought it looked messy. I chose the Cross of St James as he is the patron saint of Spain and the namesake of a prestigious order in Portugal, demonstrating the strong links between the two regions, and the steadfast Catholicism of the united crown. The remainder of the flag is similar to that of OTL Spain (though looks a bit like Austria).