The two 19-year-olds played together at Fulham and will now be turning out for Brendan Rodgers' Celtic next season.
Dembele enjoyed a remarkable breakthrough season at Craven Cottage last term, missing just three Championship fixtures and scoring 17 goals in all competitions after becoming a regular under Kit Symons and his replacement Slavisa Jokanovic.
That form at the age of just 19 alerted numerous clubs in Britain and Europe to his talents, but it is Celtic who have managed to pull off something of a coup by persuading him to move north of the border.
The Bhoys success in snaring Dembele has clearly delighted the French starlet's former teammate Roberts, who was the first to welcome the forward to Parkhead.
Big signing!! Good to play alongside you again bro.. Welcome https://t.co/tIOymvDNw8— Patrick Roberts (@patrick7roberts) June 28, 2016
The winger tweeted: "Big signing!! Good to play alongside you again bro... Welcome."
Roberts and Dembele spent three years together in London, breaking through into the first-team picture around the same time, and both played significant bit-part roles in the 2014-15 campaign before Roberts' move to Manchester City, with the pair making 20 and 15 appearances respectively in all competitions.
With Roberts to remain on loan at the Hoops until next summer and Dembele having signed a four-year deal, the teenage pair can now look forward to striking up a partnership on the pitch once again in green and white next season as Rodgers' exciting revolution at Parkhead continues.