Barack and Michelle Obama

The former United States President and First Lady - who have daughters Malia, 25, and Sasha, 22 - have been married since 1992.

Michelle attributes their continued happiness to the couple's mutual respect for one another.

The 59-year-old author told Gayle King: "You don’t do it because it’s easy. You do it because you believe in it. You believe in the other person. That’s why it’s so important to marry someone you respect. It’s important to marry someone who is your equal and wants you to win as much as you want them to win.”