The World Cup winner joined the Blaugrana from Paris Saint-Germain in the summer of 2003 and went on to win trophies galore during his five years in Catalonia.
For most of his time at Barcelona, Ronaldinho was the finest footballer on the planet and he won the coveted FIFA World Player of the Year award in both 2004 and 2005.
“Ronaldinho was responsible for the change in Barca," the six-time Ballon d'Or winner previously said. "It was a bad time, and the change that came about with his arrival was amazing.
“In the first year, he didn’t win anything, but people fell in love with him. Then the trophies started coming and he made all those people happy. Barca should always be grateful for everything he did.”
Ronaldinho helped kickstart Messi's incredible career at Barcelona and the two have remained friends ever since.
And the two South American superstars finally reunited before PSG's Champions League match versus RB Leipzig on Tuesday evening.
Ronaldinho was a guest of honour at the Parc des Princes and prior to kick-off, the pair embraced by the side of the pitch.
Take a look at the beautiful moment here...
Video: Messi & Ronaldinho reunited before PSG v Leipzig
You absolutely love to see it.
For Barcelona fans, the sight of arguably the club's two greatest ever players hugging will be enough to start the waterworks.
As most Cules will fondly remember, Ronaldinho was the man who assisted Messi's first ever goal for the Blaugrana versus Albacete in 2005.
That moment really was the start of something special, with the Argentine going on to score another 671 in Barcelona's colours over the course of 16 memorable years.