We will never know the largest star in space. We can only tell you what is the largest star discovered to this date. The Universe is simply too vast to say that what “WE” found is the largest star in space.
That is Stephenson 2–18
Stephenson 2-18 (St2-18) is a red supergiant located in the constellation Scutum. Also catalogued as Stephenson 2-DFK 1 and RSGC2-18, it is the current record holder for the largest star known, with a size 2,150 times that of the Sun.
How big is Stephenson 2-18, among the largest stars in the known universe? It would take earth's fastest jet over 500 years to travel around. It would take almost 9 hours at the speed of light. Its circumference equals the orbit of Saturn.
The star is located at a distance of 18,900 light years from Earth. It is a member of the open cluster Stephenson 2.
So, as our telescopic technology or any revolutionary technology, let us pear deeper into space this we will find out that there are stars even bigger than Stephenson 2–18. It's just a matter of time and innovation.