Mrs Brooks told the Leveson Inquiry earlier this year that Mr Cameron signed some of his missives to her 'LOL' - mistakenly thinking it meant 'Lots of Love' rather than 'Laugh Out Loud'.
Both of the messages disclosed by the MoS were sent in October 2009, shortly after Mrs Brooks left her job as editor of The Sun and became chief executive of News International, which owns the paper.
More top news
Philippa has the Bank Holiday weather for the east
Philippa has the Bank Holiday weather for the west
Philippa has the latest weather update for the east