I had raised this topic few months ago based on what is said in thiruvalangattu cheppedugal :
"Surandha mulai paal magavodu pirintha thaiyal "
(The new inscription quoted by GR is the second such evidence. Mr.GR : Is is possible to reproduce the full text of RN's article by scanning or something ? Looks very interesting...)
I even tried to write an article based on this argueing that it might be rajaraja - That aptly explains his love for his sister (akkan) and why mathuranthaka took the throne. You can find some discussions on this in archives.
But the same thiruvalangadu cheppedugal also says later that people wanted arumozhi to crown and he sacrificed the thrown for mathurantaka. Also, some of kundanthai's records are proving that this theory is not very strong... This needs further research.
Have you all read about gangai kondan thread I wrote a few months ago ? The supposed brother of rajendra ? It is another grey area in chola history...