The stats bear it out - Europe's aristocrats are practically joined at the hip in terms of achievements in this competition.
And the winners tomorrow's clash on Lansdowne Road gets the chance to put real separation between them
Both Leinster and Toulouse proudly brandish four stars on their jersey to represent the joint record they hold in terms of Heineken Cup/Champions Cup title wins.
They have both reached the semi-final stage for the 11th time. They have played each other 11 times - only Munster and Castres have done so more - and Toulouse are edging the win tally, six to five.
Dig a little deeper and the similarities go on. Leinster have played 166 games, winning 112. Toulouse? Played 164, won 111.
They've both drawn five matches over the years and, in terms of losses, Toulouse have 48 - one less than Leinster.
In terms of points for, Toulouse have scored 84 more than the Blues. Leinster have conceded just 10 more points than the Red and Blacks over the years.
The Top 14 leaders have won more semi-finals than they've lost - six to four - while Leinster haven't (four to six).
"You’ve got this real balance of experienced international players, players from overseas and this young and vibrant local-born group of players like Dupont, Ntamack, Bezy and Guitonone - there are some outstanding backs in there," warned Leinster senior coach Stuart Lancaster.
"Their ability to score tries in so many different ways - they can overpower you, they can beat you on the counter-attack, their ability to keep the ball alive and generate successions of tries on momentum.
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"If you look at the rankings of who has made the most line-breaks in the Top-14? it’s Toulouse.
“Who’s made the most metres? It’s Toulouse. Who has the most defenders beaten? It’s Toulouse.
“They’re just have an unbelievable chemistry in how they create momentum in attack.
“They have a real solidity in defence now as well which really showed it’s worth against Racing in the quarter-final.
"You can see by how many tries they've scored this season, it's a big week for us in terms of our defence, there's no doubt.
"But also, it's not generating opportunities for them to launch their counter-attack by being effective with the ball as well."
That's something Leinster managed to do well when the sides met at the RDS in January and limited the visitors' attacking opportunities.
It was a big improvement on when the sides met in Toulouse in October, with the hosts producing a famous victory.
And, perhaps crucially, Leinster are the reigning champions. Toulouse last lifted the trophy in 2010.
Plus Leinster are playing at their home away from home, at the Aviva Stadium.
"It's a completely different scenario from last year," insisted Lancaster.
"We're the champions, we're the hunted rather than the hunters and that makes the difference.
"But we're confident in our ability to turn it on for a big game. We'll need to this week."
They didn't manage it in the quarter-final - also at the Aviva Stadium - against Ulster, but Leinster displayed impressive control in the final 10 minutes to see themselves home.
Johnny Sexton was yesterday named in the side, having missed the Ulster game, and that's a big boost - as long as he is fully fit after a quad injury.
Devin Toner, Robbie Henshaw and Rob Kearney are also back to full fitness in a case of excellent timing, while the ever-dangerous James Lowe starts on the wing as Jamison Gibson-Park is injured.
"It's going to be a fantastic game of rugby against a high-quality team, who we’ve got huge respect for.
“You only have to look at their track record of results since we played them in The RDS.
“They’ve won consistently since then, other than the Toulon, which they sent pretty much their second-string out for that.
“Even the weekend game against Clermont, to come back from 44-40 down with ten to go and won it 47-44.
“The quarter-final against Racing, down to 14 men with 60 to go and won away from home.
“It is a proper challenge”.
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