According to Michael Ullmann writing in the June 2004 issue of SAM, "there are strong grounds to indicate that Erich Hartmann's last machine was a Bf 109 K-4". This is a somewhat surprising assertion given that there is no credible evidence that Hartmann ever flew a Bf 109 K-4. Toliver and Constable's "The Blond Knight..." can be discounted as an accurate reference since the authors did not have his Flugbücher or the unit KTB for the 1944-45 period.
The much repeated Bf 109 K-4 "profile" was originated by Karl Ries in his "Luftwaffe Camouflage and Markings" series from the 1960s and '70s. He had a made-up colour drawing of a Hartman Bf 109 K-4 complete with an oak wreath, and the 352 Abschüsse on the rudder. It simply beggars belief that the ground crew could have taken the time to paint the 352nd Balken on the rudder, then set fire to the machine! Pure fiction. But this was picked up by every subsequent book and decal maker as fact, a myth still pedalled by self-appointed 'experts' on the net (such as Brendan804 on warthunder.com) and the like today..
The last known Hartmann machine we have any evidence for is the well-known photo of him, supposedly taken in mid-April '45, standing by his Erla-built Bf 109 G-10 machine -see below. This was allegedly taken on the occasion of his 350th Abschuß. A more recently discovered image (below) shows a little more than the red heart and part of the Gruppenkommandeur's Doppel-winkel- this G-10 apparently features the tulip marking. This variant was also the "hottest" Bf 109 then available, so no surprise Hartmann flew one and that it was in fact most likely to have been Hartmann's last aircraft..
On the other hand - playing devils advocate here - there is photographic evidence ( see JG 52 in Deutsche Brod from Japo) indicating that the Stab JG 52 had Bf 109 K-4s with tulip designs & that as Hartmann's I./JG 52 shared a field with them the chances are he might well have flown one. According to Michael Ullmann then "there are strong grounds to indicate that Hartmann's last machine was a Bf 109 K-4". However the only 'fact' Ullmann cites in support is rather nebulous; high ranking & highly decorated pilots invariably received the latest equipment in an effort to maintain an advantage over their adversaries- rather over-looking the fact that the K-4 was proposed as an up-dated fighter-bomber variant. No matter either that the chaotic conditions in German manufacturing in early 1945 meant that machines were leaving 'factories' with little or no quality control being exercised - there is an account in the JG 300 history from a Bf 109 pilot ferrying K-4's minus instruments, oxygen etc etc. Ullmann 'suggests' Hartmann flew a K-4 (with tulip) in the last WNr batch 334xxx/335xxx which would have been finished in 75/83 with an 82/83 tail unit. Quite why a so-called Luftwaffe colours 'expert' would want to start or perpetuate this myth I've no idea. I've had this discussion with both Barbas & Lorant who both interviewed Hartmann & pored over his surviving log book; the last of Hartmann's machines we actually know anything about was a Bf109 G-10. Incidentally the highest score seen/photographed on any of Hartmann's (known) rudders was 121.
Two nice and rarely seen views of Hartmann's 7./JG52 G-6 "White 1" seen in late 1944 in Hungary