Singapore's selection as the host of the 28th Southeast Asian Games of 2015 was announced in 2011 during the 26th Southeast Asian Games, held in Indonesian cities Palembang and Jakarta. Singapore had previously been nominated to host the event in 2007 and 2013, but turned down both opportunities citing costs associated with the construction of the new Singapore Sports Hub.

Based on the above article, answer a question. How many times was Singapore nominated to host the event?
2