What to call Bill Clinton if Hillary wins?

If the results of the US presidential elections favour Hillary Clinton this week, the Democratic presidential nominee will become the first female president in US history.

That poses a tricky question. What's the best way to refer to the president's husband, Bill Clinton, especially if he is a former president himself?

There have only ever been male presidents in the United States with female spouses. And just like Hillary Clinton in the past, they are referred to as the "First Lady."

It is common to use the honourific title of "president" for anyone who has served in the post, even after they leave office. However, as there would be two people that hold the title in the first family, it would create massive confusion.

The Bush family went through a similar situation with the 41st president George HW Bush , and his son, George W Bush who was elected as the 43rd US president.

"We had President Bush and former president Bush, so when they were together, they were introduced that way, and the Clintons will be introduced the same way as well," said White House Historical Association expert Allida Black.

Lisa Grotts, a certified etiquette expert, said that the issue of how to address a male spouse is seen at the state level.

"In the US, we have six female governors, and their husbands unofficially go by First Gentleman. But there are no rules for presidential spouses," Grotts said.

"Once a president, always a president and that will always be his title for life."

Last year, when US President Barack Obama opened the official Twitter account for the President of The United States (POTUS), Bill Clinton was quick to enquire on the social media platform, if the username would stay with the office. Obama promptly tweeted a response.