I’ve been giving it a lot of thought and I have realized that you are my Kryptonite. Me? Oh, uh… No, I mean, my feelings for you. I’ve never felt like this about anyone in my life… I didn’t know that there were this many feelings to even be had.
Allura pilots the Black Lion and gets annoyed when she finds out Black is hiding something from her. It's even worse when she finds out about Shiro. After some arguing with her, the Lion lets her see it. It's over an hour later when the others come looking for her. She's red faced and flustered. Black was hiding treasured memories of Shiro gushing about 'this most beautiful princess' to her.