Near the end of WoT Book 13 "Towers of Midnight", Mat & Thom are conversing with
Moiraine, bringing her up to speed on events that occurred during her captivity.
There we see the following exchange between her and Mat:
"Elayne is Queen, then?"
"Sure is. Her mother was killed by Rahvin," Mat said.
"So you told me."
"I did? When?"
"A lifetime ago, Matrim," she replied, smiling.
Given that she "died" prior to Rand attacking Caemlyn, what conversation is she referring to?
Note: The preferred answer would include the chapter and page where it occurred, but honestly I'm just trying to sort out in my mind what in the world she's talking about.