United Kingdom, Sept. 23 -- John Legend thinks mutual "support" has been the secret to his marriage.

The 46-year-old singer has been married to model Chrissy Teigen since 2013, and although they've faced lots of challenges over that time, the celebrity couple remain as strong as ever.

Asked what's been key in their marriage, John told Us Weekly: "Just support each other and love each other. Have each other's back.

"We've been through it all together - so much joy, but also pain and challenge and grief.

"I think knowing that we have each other's back and support each other through it all is - you know, when you have that as your foundation, it's everything."

John is currently on tour to mark the 20th anniversary of his debut album, Ge...