Will Smith and Jada Pinkett
Will Smith and Jada Pinkett have been married for 18 years and together for 20 Kevin Winter/Getty

They are one of the strongest couples in Hollywood but Will Smith admits that he and wife Jada Pinkett Smith have found their marriage to be "excruciating" at times. Over the course of their 18-year marriage, Smith and Pinkett Smith have been plagued by divorce rumours but they continue to defy the critics.

Smith, 47, tied the knot with the Gotham actress in 1997 after two years of dating and they share two children, Jaden, 17, and Willow, 15. There have been many reports of trouble within the marriage as well as cheating allegations, all of which were denied, but Smith says he and Pinkett are determined not to call it quits.

The Men In Black actor told Entertainment Tonight: "We've been married 20 years and we've been asking ourselves [what's the secret to marriage] and really at the end of the day it's just not quitting. You can't expect it to be easy, it's like our marriage was the most difficult, gruelling, excruciating thing that we have ever taken on in our lives. And you know we're just not quitters."

When asked what the key is to maintaining a successful and healthy marriage, Smith replied: "If there is a secret I would say is that we never went into working in our relationship. We only ever worked on ourselves individually, and then presented ourselves to one another better than we were previously."

Will Smith and Jada Pinkett
Will Smith and Jada Pinkett share children, Jaden and Willow, while Smith has son Trey from a previous marriage Jamie McCarthy/Getty Images for Mercedes-Benz

In August, a fresh spate of divorce rumours emerged but Smith, who usually maintains a wall of silence, shut down the critics via Facebook. The Oscar-nominee wrote: "So, in the interest of redundant, repetitious, over & over-again-ness... Jada and I are...NOT GETTING A DIVORCE!!!!!!!!!!!!! I promise you all - if I ever decide to divorce my Queen - I SWEAR I'll tell you myself! ‪#‎Dumb‬ People Should Have to Wear Scarlet D's."

The couple have also been subjected to years of speculation that they have an open marriage and are allowed to sleep with other people. But Pinkett Smith, 44, denied this, writing on Facebook: "The statement I made in regard to, 'Will can do whatever he wants,' has illuminated the need to discuss the relationship between trust and love and how they co-exist... Will and I BOTH can do WHATEVER we want, because we TRUST each other to do so. This does NOT mean we have an open relationship...this means we have a GROWN one."