The sculpture, made out of plastic bricks, has toured 10 UK cities throughout the summer getting bigger at each location as thousands of record-breaking kids contributed their own bricks. The sculpture was completed on Tuesday 9 October, in the morning, by the X Factor finalist, bringing the total tally of participants to a whopping 18,566.
The official record broken was for the most participants to build an interlocking plastic brick structure and Stacey completed the record on the banks of the River Thames in front of London's iconic Big Ben.
The final structure weighs one ton - the same size as an average polar bear. It is three metres high, three metres wide, made up of 250,000 bricks and took over 500 hours to complete.
Official adjudicators from Guinness World Records were on site to verify the attempt and present the certificate confirming the record.
Stacey, who kick-started the record attempt in Glasgow said: "The participation of the UK in this record attempt has been incredible. It's so exciting to see the final sculpture after placing the first brick down back in August. Everyone has really got behind the attempt - my uncle even came to see me in Glasgow and added a 20 year old brick that was his as a child."
The record-breaking alien was designed and directed by Kevin Cooper. He said: "It was a huge challenge to design and build an alien sculpture of this size within the available timeframe but luckily I had the help of over 18,000 kids across the country as my assistants! Everyone who was involved should be very proud of their efforts, which have made record-breaking history."
The alien that has been built is named 'Bloxx' and features in the forthcoming series of Ben 10 Omniverse, which premiered on Cartoon Network on 6 October.
The cities that took part in the world record included: Glasgow, Sheffield, Notingham, Manchester, Milton Keynes, Birmingham, Newcastle, Bristol, London and Kent.