The singer marked the anniversary by sharing a throwback photo of the couple holding hands.
"21 years today," she captioned the Instagram snap.
The remarkable day must have been bittersweet for Celine and Rene, with the music producer being diagnosed with terminal throat cancer in 2013.
The 27-year-old recently took a year hiatus from Las Vegas residency to look after her husband during his time of need.
The duo met when Celine was just 13 years old and despite their 26 year age difference, they wed in December 1994 when she was 26.
Rene first battled cancer in 1999, and was declared cancer-free the following year. Sadly, in 2013 the illness returned and in 2014 he discovered the cancer was terminal.
"I’m amazed by him ever more than ever before. I was in love with him the first day, and today I find strength and I learn so much from him," Celine said on Good Morning America.
The couple are looking forward to a relaxing Christmas with their three children René-Charles, Nelson and Eddy.
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