The Prince was really excited and didn't quite remember that Riku couldn't read very well and wouldn't just read it over his shoulder, or thought to read it out loud the first time.
So his reading of the invitation and passing it off to Riku to read the letter was punctuated by excited little gasps and almost upsetting his tea and snacks by squirming. "Oh my gosh! Oh! Haha...he called you Mister Riku." He waited a second and when Riku didn't seem to be having the same reaction as him he felt awful and moved so he could kiss his cheek in apology.
"I am sorry, my love. Um....do you want to?" He pointed to the card. Did he want to try to read it or did he just want Sora to read it?