Give a stream of consciousness and then the final answer. When the Silence see the Doctor, they stir and begin to escape confinement; it is part of a trap arranged by Kovarian. The Silence then overload everyone's eyedrives, causing effects varying from great pain to death; Madame Kovarian not excepted. The Doctor and River escape to the top of the pyramid while Amy and Rory fight off a wave of Silence, and Amy realises who Rory is. Madame Kovarian dislodges her own eyedrive as it begins to overload, but Amy forces it back in place with the intention of killing her as revenge for her kidnapping baby daughter (Melody Pond). Amy and Rory regroup with River and the Doctor. River tries to convince the Doctor that this alternative frozen timeline is acceptable, but the Doctor explains that all of reality will soon break down if the fixed point event does not occur. River puts out a distress call that the Doctor is dying, and the skies fill with grateful friends arriving to help. River ways that if she has to kill him she will suffer just as much as the entire universe dying from time breaking down. The Doctor marries River on the spot and whispers in her ear, declaring that he told her his name. He then requests that River allow him to prevent the universe's destruction. The two kiss, time restarts, reality returns to normal, and the Doctor dies.

Based on this passage, what did doctor who whisper to river song?
The relevant sentence in the passage is: The Doctor marries River on the spot and whispers in her ear, declaring that he told her his name.
So, the final answer is his name.