For those of you keeping count, it means Three may well have the widest 5G coverage by the time the year is up. EE now only offers 5G in six cities, and promised a total of 16 locations will have 5G before the end of the year.
The launches are part of Three's £2 billion ($2.5 billion) 5G infrastructure investment commitment.
The 5G network will make its debut in London in August in the form of a home broadband service, Three announced on Monday.
Three claims it has "more than twice as much 5G spectrum as its closest competitor", meaning it can deliver significantly faster speeds for its customers.
Dave Dyson, CEO at Three, said: "It's clear that consumers and businesses want more and more data".
"We have worked hard over a long period of time to be able to offer the best end to end 5G experience".
EE has already said that peak speeds on its 5G network right now could exceed 1Gbps, so if both EE and Three are right, then that would mean peak speeds of over 2Gbps on Three's 5G network, which is seriously fast.
We don't know everything about Three's 5G launch yet, but the company has promised to provide more details about handsets and pricing in July, so stay tuned.
United Kingdom consumers are predicted to consume 13 times more mobile data in 2025 than today and 5G is hoped to cater with this extra demand.
This will be achieved through deploying more 4G spectrum, converting 3G spectrum to 4G and using advanced antenna technology, according to Three.
Other promises are internet speeds comparable to fibre broadband with "plug and play" 5G hubs, as well as the goal of expanding 5G services across 80 per cent of its network traffic over the next three years. Vodafone for comparison has just 50Mhz of 5G spectrum, while EE and O2 have just 40MHz.
We'll bring you more news as we get it.