mostrasteis
-you showed
The word mostrasteis is the preterite form of mostrar in the second person plural.
See the full mostrar conjugation

mostrar

El comportamiento que mostrasteis en vuestro plan de boda no fue profesional e inaceptable.
The behavior you two displayed with your wedding planner...was unprofessional and unacceptable.
Después de la hospitalidad que me mostrasteis ambos, esto es lo menos que puedo hacer.
After the hospitality you showed me, this is the least I can do.
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