"Happy Birthday @lionelrichie" the country superstar captioned the throwback, which shows the two of them sitting in a bedroom with recording equipment behind them. "You have my endless love!!"
WATCH: Shania Twain rocks a bikini and sheer cover-up in video from tropical vacation
The Say You, Say Me singer, who turned an incredible 72 on Sunday, returned the love by commenting on the post. "Love u Shania …" he wrote.
Fans were in agreement over the love being shared, flooding the comments section with birthday wishes of their own and sending a cascade of loving emojis their way. "My favorite song, i still listen to it from time to time," one person commented.
The shot of the two comes from when they recorded their duet
The "endless love" is a reference to one of Lionel's most popular songs, 1981's Endless Love from the movie of the same name, a duet with Diana Ross. The track became one of the most successful songs of the 80s in the United States, spending several weeks at number one and becoming one of the most well-known duets of all time.
It was in 2012, however, when Lionel recruited Shania to cover the track with him for a new version which featured on his tenth studio album, Tuskegee. That version leaned more towards Shania's country roots. Her throwback post is a still of the two from the song's cover art.
The singers have been friends for quite a while, especially since their collaboration
The tribute comes not long after Shania's Las Vegas residency announcement, which instantly revived interest in her first big hits as we wait for them to hit the Vegas stage.
Lionel, meanwhile, celebrated his birthday in an intimate way, involving his three children, his girlfriend Lisa Parigi, and Joel Madden. The legendary musician's birthday cake was even made as a bust of his face, with a "Hello" spelled out in icing, a callback to another very popular song of his.
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