While the previous B4 was based on the two-door BMW 4 Series Coupé, its successor will take the new BMW 4 Series Gran Coupé as its basis.
Spy shots released last year showed an obviously uprated 4 Series Gran Coupé being tested on public roads, lending credence to earlier claims that Alpina's next unveiling would be a four-door, rather than a traditional coupé.
The tip came from an unidentified source on the popular Bimmerpost forum who claimed to have access to future product plans "compiled from various leaks within the BMW organisation".
According to the dates outlined, the new B4 will be introduced in March 2022 as BMW ushers in a new four-wheel-drive 430ix variant of the G26-generation 4 Series Gran Coupé.
It remains possible that a two-door version could follow shortly after.
Given the technical similarities between the previous-generation B4 and the current 3 Series-based B3, we already have a good idea of the new four-door's make-up.
The B4 will no doubt share the B3's twin-turbocharged 3.0-litre petrol straight six, sending 462bhp and 516lb ft to both axles through an eight-speed automatic gearbox tuned for quick shifts and improved response.
A diesel version, badged the D4 Gran Coupé, will likely follow soon after.
Performance figures will be broadly comparable, too, given the 4 Series Gran Coupé and 3 Series are closely matched in size and weight, so expect a sub-4.0sec 0-62mph time and a top speed approaching 190mph.
The B4 will, as did the previous generation, essentially fill the gap between BMW's own M440i xDrive and full-fat M4.