Last Saturday (Feb 29), American actress Jessica Biel was spotted by the Daily Mail in Beverly Hills without her wedding ring on.

It sparked speculation that her marriage to singer-actor Justin Timberlake was on the rocks after he was spotted holding hands with actress Alisha Wainwright last November.

The Can't Stop The Feeling! singer apologised to Biel in an Instagram post in December, admitting that he suffered a lapse in judgment and regretted his behaviour.

The couple, who married in 2012 after five years of dating, have a four-year-old son, Silas.

On Tuesday, Timberlake, 39, took to Instagram to wish his wife happy birthday - the 7th Heaven (1996 to 2007) actress turned 38 that day.

He wrote: "Happy Birthday to the LOVE of my life... A new adventure every day and a treasure to me. I can't wait to share many more of these with you.

"Thanks for putting up with me when I smell funky after a round of golf or, when I smell funky in general. You are the mostest (sic) of the mostest, my love! I adore you."

The post was accompanied by four photos of the couple together, including one taken last Halloween when Biel dressed as Timberlake from his days with boy band NSync, while he was dressed as a huge microphone.

Biel then commented on the post: "As you always say, you can't be funky if you don't smell funky."

She also shared on Instagram two photos of her and Timberlake celebrating her birthday - he was hugging her in one. And her ring was clearly visible in the other photo.