The French midfielder has signed a four-and-a-half-year deal with the Spanish champions and will go straight into the first team when the transfer window opens on the 1st of January.
The fee Pompey has received for Diarra is undisclosed but is confirmed to be higher than the £12.7 million that was paid by Inter Milan for Sulley Muntari and is rumoured to be around £20 million.
Whatever the fee, it represents Pompey's highest ever transfer fee received for a player, having made a huge profit on the £5.5 million paid to Arsenal for a player of superb quality.
Diarra made his farewell appearance for Pompey at the Reebok on Saturday and personally came over to thank the fans after the match. I'm sure that there won't be a single Pompey fan who will begrudge such a talented player a move to probably the biggest football club in the world.
He is definitely the best player I have ever seen to have worn the Pompey blue, even though his stay at Fratton Park has been less than a year long. I'm also glad he is moving to a club deserving of his talents, rather than Manchester City or Tottenham.
As a follower of Spanish football I think Real needed to bring in a player such as Lassana due to their injury ravaged squad which includes a long-term injury to his namesake Mahamadou Diarra who usually plays in the defensive midfield role. To avoid confusion, Lassana will wear the name "Lass" on the back of his shirt.
Diarra is going to have to influence the Madrid midfield pretty quickly as the current champions are currently lagging in 5th place in La Liga and are already 12 points behind leaders Barcelona, having shipped 26 goals in the league already (that's only two less than Pompey having played two less games).
We will miss a player of Diarra's quality but if what Tony Adams says is true then we now have substantial funds to find a replacement for him and to strengthen to team in other positions such as the wings and at the back.
Thanks for your contribution Lassana, and I'm sure the rest of the Pompey fans will join me in wishing you all the best at the Bernabeu.