The king is planning to stamp his name into the great book of history by subjugating the Ptolemaian Empire in a glourious Alexander-like campain. It's immortality in the memory of mankind, that he wants. He's not a modest man, as you know.
About the dangers coming with his plan he naturally thinks not. He's also not really a clever guy.I don't know what will happen, but I'm shure there will come hard times for Geraint.
I don't now the word "duped" means, so I'm not shure, if this answers your question properly.