Diaz turned 46 on Thursday, so Madden, 39, shared a photo of the two near a lake. It appears to be an older photo, since the two are both bundled up for winter.
"Happy Birthday Baby. There’s so much to write, so many things that make me so proud of you and how special you are," Madden wrote in the caption. "Thank you for being the best friend and partner to me and taking this journey of Marriage. The way you live your life everyday, and your compassion for the world shines thru in your eyes and you inspire me to want to be the best man I can be in this lifetime. You’re the realest. I’m so grateful to be yours Always & Forever, and to call you my One & Only. True Love."
The two have been married since 2015, and are rarely seen in public. Diaz does have her own Instagram page, but she has not used it since Election Day 2016. In July 2016, she celebrated the release of Good Charlotte's first album in six years by sharing what makes her proud of her husband.
"He makes me proud everyday.. One day it might be how generous and giving, another how gentle and thoughtful," she wrote. "Or when he is fiercely protective of the people he loves and cares about... And everyday single day I am so incredibly proud of his integrity as a human being."
PEOPLE reports that Diaz was seen out with sister-in-law Nicole Richie and Zoe Saldana at the Los Angeles restaurant Il Segreto Ristorante Belair for a birthday dinner on Tuesday night. They were joined by Saldana's husband Marco Perego. Richie's husband is Madden's identical twin brother Joel.
Diaz has not appeared in a film since the 2014 Annie remake, and now spends most of her time writing wellness books. In 2013, she wrote The Body Book, which was followed three years later by The Longevity Book.
Back in March, Diaz made headlines when she confused fans over her possible retirement. Her friend and The Sweetest Thing co-star Selma Blair said Diaz told her she was "done" with Hollywood. However, Blair later took to Twitter to say Diaz was "not retiring from anything" and she was retiring from being Diaz's "spokesperson."
In a plot twist fit for the romantic comedies that made Diaz a star, she told Entertainment Weekly she is "actually retired."
"I’m semi-retired, too, and I am actually retired, so I would love to see you ladies," she said in an interview alongside Blair and Christina Applegate.
"[Madden and Diaz] are both very happy living the quiet life," a source told PEOPLE in March. “The quiet life she lives now with Benji, she wanted for a long time.”
Diaz and Madden do not have any children together, but a source told Us Weekly they have been trying to have children since they married.
“It’s been a long, hard struggle with many ups and downs,” the source said in January. “Cameron would love more than anything to be a mom.”
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