The couple separated in 2009 after Brown assaulted the 'We Found Love' singer, resulting in him being sentenced to five years' probation and six months of community service.
The former lovers have appeared to mend their relationship in recent times, with Rihanna easing a restraining order against the 22-year-old and claiming she "would never wish anything horrible" on him.
Rihanna and Brown also started following each other on Twitter in May, but have not written to each other as of yet.
However, the duo caused a stir online when Rihanna tweeted "'ll always love u #1LOVE" just two minutes after Brown wrote "Love U more than u know!" yesterday (December 29).
No context was provided for either star's message, prompting talk that they may still be in contact with each other in secret.
Rihanna was romantically linked to Usher earlier this week when the 'Caught Up' performer admitted that they have kissed.
Watch the video for Rihanna's 'You Da One' below: