After a highly impressive maiden season in Germany with Mainz, Diallo was a wanted man this summer.
English Premier League giants Arsenal and French Ligue 1 heavyweights Lyon were both in the race to sign the 22-year-old, but Diallo eventually put pen to paper on a five-year deal at the Signal Iduna Park after talking to Favre.
Watch: Diallo makes a winning debut with Dortmund
"He knew quite a lot about me," explained the former Monaco man, who will be with the France Under-21 squad during the international break.
"When he met me, he spoke to me as if I were already his player, I liked that. We talked tactics, technique, my season, his season, a lot of things. It was all very natural. Our first meeting went well."
Diallo's first steps in yellow-and-black have also been positive. After the Matchday 1 win over RB Leipzig, Favre's men picked up a point with a battling goalless draw at Hannover on Matchday 2 before Diallo teamed up with the France Under-21 squad.
After the international break, he and his BVB teammates will open Matchday 3 with the visit of Eintracht Frankfurt before they travel to Belgium to face Club Brugge in their opening UEFA Champions League group stage game.