The forward today revealed his secret heartache and thanked the club's fans for their support at St James's Park.
Perez had created Kenedy's second goal on Saturday with a powerful run forward.
The result lifted the club up to 13th in the Premier League table.
"Last week has been a very hard week for me," Perez tweeted. "Last Wednesday my grandma passed away, she was like a second mother for me.
"Saturday’s win was for her ... and THANKS to all the fans for the support you showed, it was too much needed for me after some sad days. We keep fighting "
United thanked Perez, 24, for "giving everything in difficult circumstances".
Newcastle replied: "Our sincere condolences to you and your family, @AyozePG. Thank you for giving everything in difficult circumstances."