It'll come in autumn most likely. Top Gear and Grand Tour will work in tandem now, I think. Top Gear s24 is coming this summer. So don't expect Grand Tour until Top Gear season 24 finishes.
Sorry. I keep forgetting that you guys have summer a bit later than us. Over here in India it has already started. We don't really have a proper spring season, here summer starts in March.Top Gear Series 24 actually starts next month on the 5th which technically speaking is the spring or very close to it.