Nick tweeted a picture of 19-year-old Bobbi wearing the giant sapphire stone surrounded by diamonds today, sparking rumours of an engagement.
It was accompanied by the caption, 'just a jewelry/gift for the sweetest thing in the world.'
Impressive bling: Nick Gordon tweeted a picture on Monday of his girlfriend Bobbi Kristina wearing a spectacular sapphire and diamond ring
Getting closer every day: Nick accompanied Bobbi to the premiere of Sparkle which was Whitney's final filmBobbi responded by tweeting: '(: urthee best boo ! I love you, thank youuu (:(: surprise is right , i love it!'
The spectacular jewellery is almost identical to the one worn by the late Princess Diana and now worn by Duchess Catherine of Cambridge.
Bobbi and Nick lived together as brother and sister for more than a decade before Whitney's death.
Engagement ring of just bling? Nick wrote that the ring was 'a gift'
The chart-topping singer took Nick into her home at the age of 12 when his father went to prison and his mother was unable to take care of him.
Mother and daughter: Whitney Houston attended a pre-Grammy Awards gala with Bobbi Kristina in Los Angeles on February 12, 2011
Whitney was found dead in a Beverly Hills hotel room on February 11, 2012.
The six-time Grammy award winning singer, died at the age of 48 due to an accidental drowning complicated by heart disease and cocaine use.
Nick first fueled rumours about a relationship with Bobbi Kristina in a tweet written in March, shortly after Houston died.
He wrote: 'Yea we got a little closer and what!!!'
The controversial couple have reportedly been sharing her $1.2million Atlanta home together ever since.
By the age of 30 Bobbi will have inherited everything that belonged to her iconic mother - mansions, jewellery, cars, and an extraordinary fortune.
She recently did a guest stint on Tyler Perry's sitcom For Better Or Worse.
And the mourning starlet is currently filming her upcoming reality show, The Houston Family Chroni