If the introduction is done correctly, you can follow the lead.

Yes, Germany retained the royal names as the legal surnames of everyone who had one. A friend of mine is normally 'John' "von der X", even though his official ID states his proper name is 'John' "Graf von der X von Y". In Austria it is where there are no more royal titles of any kind.

Reminds me of the true story of when the late Alan King was introduced to Queen Elizabeth II.

"How do you do, Mr. King," the Queen said.

"And how do you do, Mrs. Queen," the comedian replied.

It's said that when the young Queen Elizabeth first visited Australia in 1954 her consort, the dashing Prince Philip, Duke of Edinburgh, managed some furtive dalliances with local debutantes while HM was otherwise engaged. As, apparently, was his wont.

During a more recent visit a few years ago, the usual gaggle of Sydney socialites was lined up to meet the royal couple. Half-way down the line the Duke came to one of his former conquests, whom of course he failed to recognise. She curtsied, then smiled sweetly and in a stage whisper said one word: "Bastard!" For once the Duke had nothing to say.