Miranda Grenier is the mother of Tim's child Shane and Tim's old girlfriend from when he was on a "break" with Marion. She resides in Moose Jaw with her son Shane. In the season 5 finale she comes to Heartland to retrieve Shane from his summer vacation there after finding the video of the showdown with Tim's race horse Cisco
In Season 6 Tim and Miranda start a relationship but it soon ends after Jack has a talk with Miranda about how committed Tim will be. Tim and her met in a casino and she was a not doing too well, but was cleared after her son Shane was born.
Tim tried to crash Miranda's wedding. But Jack stopped him.