Canon Background
https://awoiaf.westeros.org/index.php/Mathis_Rowan

In-Campaign
The year was 284 AC when an enraged Mathis entered the solar of Goldengrove after his terrified wife and septa cried that some visitors from House Jasper had threatened them. Mathis quickly gathered 10 guards and entered to find a belligerent knight, a maester, and a red priest (who he mistook for an old acquaintance named Jeremy). The knight demanded and blustered and stated they had come to claim his eldest child, Berta, as a ward on behalf of Lord Jasper. Mathis explained that rather than see his daughter shipped away he had quickly secured a betrothal to the heir of House Mullendore and that she had left a week ago to be wed. He was forthright and explained that he shared his planning so openly because there was likely little that the Jasparians could do to intercede. Both the knight and the red priest insulted him and spat on the floor as they left.

Though their true identities were not known to him: Teddy Jasper, Ser Dolins, and Gregoriy Al-Tem were jailed in his cells for a night in 287AC. The trio broke loose in a daring escape and reclaimed Victorinox as they fled.