The Walkinshaw TWG Racing driver spat his Dick Johnson Racing rival off the road on the penultimate lap of the fourth Supercars race at Ruapuna.
Mostert was deemed to be at fault for the incident and was penalised, which dropped him to 17th in the result.
Kostecki labelled Mostert’s act “malicious” while DJR co-owner Ryan Story said Mostert’s comments in the aftermath of the incident were “unbecoming of a reigning champion”.
In recent days, the two drivers were pictured together with Will Brown, Jackson Walls, Ryan Wood, and Kai Allen.
It’s understood all bar Kostecki were in Toowoomba for filming of the latest Supercheap Auto Best Performing Oils campaign.
On Tuesday, Mostert spoke at a media call promoting Supercars’ upcoming visit to Townsville in July.
Asked about whether Mostert had buried the hatchet with Kostecki at the “shindig” hosted by Brown, last year’s champion said he was keen to move on.
“I guess we’ll find out at the next event,” said Mostert.
“Like any driver, you reflect on past races and in the moment you would of course do a different scenarios or change your approach, and that’s what I’ve had to do from the last event and try and reflect on myself and reflect on what I would do differently.
“No doubt, it wasn’t the outcome I definitely wanted in New Zealand, which I’ve been pretty open about. You never want to see any competitors go off the track in the way that did. That’s all on me.
“I’m looking forward to the next event and try qualify up there and get some more results for our team. We lost a lot of points over that one. Looking forward to it.
“Brodie is a champion of our sport. He gives his all on and off [the track] and I’ve got enormous respect for him and it was good to go see him after the event and hopefully put it behind us.”
Brodie needed to make that pass and it’s resulted in DRAMA between him and Brodie Kostecki!! #RepcoSC #Sueprcars pic.twitter.com/fKX05OeXaG
— Supercars (@supercars) April 19, 2026
Mostert’s brewing rivalry with Kostecki is the latest in a series of feuds between drivers.
The animosity between Ryan Wood and Broc Feeney continues to bubble away behind the scenes after their Adelaide Grand Final run-in.
Mostert said there has been a noticeable year-on-year increase in intensity, helped in part by the Finals Series.
“I think everyone with their helmets on, everyone’s got a rivalry against someone,” said Mostert.
“It might not be so much talked about off track, but definitely from last year to this year I feel like our racing has really taken a gear.
“With the Finals format and cut-off lines and all that sort of stuff and focusing on all these different stories, no doubt all us drivers feel that pressure.
“In those pressure moments it either makes you or breaks you.
“I think it’s pretty cool that we have these elements to talk about in our series where previous years we’re talking about one or two guys that might have to fight for the championship throughout the year. Now it’s all unknown.
“It’s exciting, it’s exhilarating, the drivers feel the pressure of the teams and that’s all just coming out a bit more. Other than trying to add speculation and add rivalry, they’re already there. We just probably don’t necessarily talk about them so much.”
The Repco Supercars Championship resumes at Symmons Plains for the Tasmania Super440 on May 22-24.
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