Why was the Queen of England worried when the waiter dropped the tray at the official dinner?

Question

Chetan was having a cup of tea in a restaurant when he called the waiter and told him that there was fly in his tea. Startled, the waiter took the cup and brought a fresh cup of tea. Moments later, Chetan called the waiter again and told him that it was the same cup of tea.

How did he come to know ?