Greater London is marginally bigger. It covers 1579 km² and had a population of 7,172,036 at the 2001 census.
The population of Riyadh is less than half as big, at 3,500,000 people. However Riyadh is physically almost as the same size as Greater London, at 1,554 km².
https://en.wikipedia.org/wiki/Riyadh