@rubicscubicle
Because he is not the 'other guests'. He is part of the wedding party. The main part.
Can someone comment on whether it's normal to not send the wedding party formal invitations in the UK? In the US, they'd all get an invitation, same as everyone else. For every wedding I or my husband has ever been in, we received formal invitations in the mail, even though we'd already been asked to be a bridesmaid/groomsman and accepted months before they were mailed.
The wedding party still needs all the basic information like locations, times, etc. that's on the invitation. If there's a choice of dinner options, the couple will need RSVPs from the wedding party same as everyone else, so the caterer has the right numbers. Plus ones are pretty standard for the wedding party, but the wording of the invitation is where people look to see whether their children are invited.
Maybe none of that applies to this specific royal wedding, but since it's the standard practice, I can see why Thomas was surprised not to receive one. Especially since so many were mailed to other guests in the US, and they'd have been mailed months before things went sideways. I wonder if Meghan didn't want to give him a +1 because she was afraid he'd bring Samantha, and thought she'd avoid the whole problem by not mailing an invitation?