President Obama drew his biggest audience ever Sunday night when 56.5 million viewers tuned in to watch his announcement that a U.S. Navy Seal team had killed Osama Bin Laden in Pakistan. The figure was more than twice the number who watched his March 28 speech on Libya -- even though it did not begin until 11 35 p.m. ET, an hour when most viewers have called it a day. Nielsen Research said that the 56.5 million figure represented the number of viewers who watched the speech live on nine broadcast and cable channels ABC, CBS, NBC, Telemundo, Univision, CNN, Fox News Channel, HLN and MSNBC. Meanwhile, CBS announced Tuesday that President Obama has agreed to give his "first and only" interview about the killing of bin Laden to Steve Kroft on next Sunday's 60 Minutes , an appearance that could set a ratings record for the venerable magazine show.