After a 13-year hiatus, BMW M's beloved CSL (Coupe Sport Lightweight) nameplate is making a belated comeback. Last used on the E46 M3, the CSL badge is reserved for BMW M's lightest, purest, and most track-focused sports cars. It hasn't been officially announced yet, but we already know the new M4 is getting the CSL treatment. BMW M has been secretive about it, but former BMW M CEO Markus Flasch has revealed some new juicy details about the lightweight sports car in an interview with Auto Motor und Sport.

When asked if he could confirm if the BMW M4 CSL is coming, Flasch referred to the car as an "open secret." That's as close as we're going to get to official confirmation.

Although BMW hasn't announced the M4 CSL yet, the former CEO was surprisingly candid, revealing that the "four-seat design [of the M2 CS and M5 CS] won't play a role." This confirms our suspicions that the rear seats are being removed to make the M4 CSL as light as possible.

Exactly how much lighter will the M4 CSL be, you might be wondering? "We are aiming for a weight saving in the triple-digit range," Flasch said, confirming that the M4 CSL will be over 100 kg, or 220 pounds, lighter than the M4 Coupe. This significant weight loss should make it even more agile and enjoyable to drive when attacking corners. But while the regular M4 is available with a six-speed manual transmission and BMW's xDrive, the M4 CSL will reportedly only be available with an automatic transmission and rear-wheel drive.

Powertrain details are still being kept under wraps, but Flasch did confirm the engine won't be electrified.

Spy shots have shown the M4 CSL will sport a redesigned version of the M4's controversial kidney grille with Y-shaped horizontal slats, as well as a larger trunk lid spoiler. Under the hood, the M4 CSL is expected to pack a more powerful version of BMW's 3.0-liter twin-turbocharged inline-six engine producing around 540 hp. The new M4 CSL is expected to break cover next year to coincide with BMW M's 50th anniversary.