The Apple Watch Series 3 was launched last Autumn and was a critical hit. We also think it has sold quite well, but we don't really know since Apple refuses to outline the numbers sold.

That's probably because the numbers wouldn't look that great up against the numbers of iPhones or Macs sold. However, we do know that Apple's wearables business - including Beats and AirPods is "as big as a Fortune 300 company" - so effectively one of the top 300 US companies. 

Tim Cook also said back in February that sales around last Christmas and in that quarter were the best ever for Apple Watch. 

If there is a new watch this year, it'll be announced at the same time as the iPhone XI, so in September. That means the Apple Watch Series 4 release date will probably be late September or early October. 

The new Apple Watch software update - watchOS 5 - was announced at Apple's Worldwide Developer Conference (WWDC) in early June. 

Apple trailed several new features in watchOS 5 including a lot of new Activity and Workout features, the Walkie Talkie app and interactive notifications. Find out more about watchOS 5 features.

It wouldn't be too farfetched to assume that Apple will change the design of the Watch, as it has retained much the same form since the very first Series 1 model launched in 2015.

The display seems to be the key specification that will be upgraded for Series 4. Straight off the back of the new iPad 9.7-inch launch, usually-reliable KGI Securities analyst Ming-Chi Kuo has issued a new report saying the upcoming Apple Watch Series 4, due out later this year, will have a 15 per cent larger display.

Along with a larger display, Kuo says the new Apple smartwatch will have improved health monitoring capabilities and a longer battery life than the current Series 3 model.

However, while Kuo says the Series 4 will come with a larger display, he doesn't say whether the size of the casing will increase too, or if Apple will keep the current size and just shrink the bezels.

Twitter tipster Ben Geskin has waded in on the debate and produced a mockup of what he thinks the new Watch will look like, based on Kuo's predictions. His design shows the same overall size Watch, but will much slimmer bezels.

However, if the battery life does increase, the Watch may need a larger casing to accommodate a larger battery. Kuo doesn't go into too much detail regarding the rest of the Watch, but he says the combination of a "more trendy form factor design", additional sensors beyond heart rate monitoring and lower prices for the older models, will have a positive impact on sales.

Despite Kuo's track record when it comes to Apple predictions, we have to take this with a pinch of salt for now until more leaks and rumours surface.

Got an Apple Watch already? Then check out the best Apple Watch accessories: Protect and personalise your watch