Michael Douglas and Catherine Zeta-Jones have shared gushing tributes to one another while marking their joint birthdays.

Both Michael and Catherine have their birthday on September 25, and this year turned 82 and 57 respectively, paying tribute to each other in adorable posts on Instagram.

Michael shared a picture of himself and Catherine on the red carpet, alongside an excerpt from his memoir One Helluva Ride!, about his stunning wife.

He wrote: "I had never fallen in love on a movie screen before. Until I saw Catherine. She was magic, in a way that went beyond beauty.

"And I was certain, as much as I had ever been about anything, that she was the one. It's the kind of moment that only comes around once in your life, if you're lucky.

"he one time that you know, without any doubt in your mind, that you're meant to be with someone. Happy Birthday Catherine! I love you always and forever!"

Catherine replied in the comments: "Thank you darling. Thank you. Happy Birthday to you too my love."

She also took to her own Instagram page to share a snap of herself and Michael sharing a romantic kiss in a swimming pool, writing: "Happy Birthday darling! A birthday kiss to my husband Michael, sharing this special day with you, is as special as the day itself. Love you."

In the comments section on that one, Michael's son Cameron - from his first marriage - added: "Happy happy Birthday to two of the greatest people I know…here's to many more years filled with Love and Happiness."

The joint birthday tributes come after Catherine opened up about the secret behind her and Michael's happy marriage, crediting their balancing of their work and personal life as one of the biggest positives.

In an interview with The Sunday Times Culture magazine, Catherine said: "Michael is, like, 'Go and do that job, that's amazing.' And then he's able to fly in and see me for a long weekend.

"Much better than waking up, going, 'What do you want for breakfast, honey?' I don't think our marriage would ever have lasted if it was like that."