In one message obtained by the Mail on Sunday, the Prime Minister thanked Mrs Brooks for letting him ride one of her horses, joking it was "fast, unpredictable and hard to control but fun".
In another the journalist, who faces trial in connection with the phone hacking scandal, praised Mr Cameron's speech to Tory conference, saying: "I cried twice."
The playful texts are apparently part of a cache of texts and emails handed to Lord Justice Leveson's media standards inquiry.
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Another cold and frosty night lies ahead, but the winter sunshine prevails for Friday.
Staying cold and frosty with plenty of winter sunshine.
Plenty of sunshine for some, but a little more cloud in the east and feeling cold