The Destiny's Child singer was wishing her producer friend Patrick 'J. Que' Smith's child a happy birthday in a sweet video message.
The video, which was posted last week (15 November), shows the 32-year-old US X Factor judge raising her left hand to blow a kiss.
It is then that a large sparkling rock is seen on her fourth finger.
Kelly has always remained private about her love life, but it is thought that she has been dating Tim Witherspoon - who is also her manager - on and off for four years.
Kelly has since remained quiet about the engagement rumours, but wrote on Twitter last night: "A smile is the best accessory that you can have."
In a recent interview with E! News, when asked if she wanted kids and marriage in the future, Kelly said: "I don't know. Too busy with the career. I do want kids, I do want to be married."
Kelly spent the beginning of this week in Dubai where she performed at a gala dinner. She is expected to return to the US on Friday for a performance in Virginia.
Watch the video of Kelly wearing a diamond ring below: