This happened during the look test for Kathryn and Alden's new Star Cinema movie. An Instagram video was uploaded on Philip Rojas' account on March 17, 2019.
Alden led the staff and crew in singing the "Happy Birthday" song as he carried the birthday cake for Kathryn.
According to the film's director, Cathy Garcia-Molina, the birthday surprise came early because, "baka hindi ka na namin makita, e!"
Kathryn, who is turning 23 on March 26, is set to take a birthday vacation with her family and friends at an undisclosed beach.
After blowing her birthday candle, Direk Cathy teased the Kapamilya actress for taking too long to think about her wish.
The young actress said, "Para sa atin lahat ito!"
Kathryn then gave Alden and Direk Cathy a hug.
On March 12, Star Cinema announced that Kathryn and Alden will be paired in a movie to be shown this 2019.
The two are set to play OFWs in the movie to be shot in Hong Kong.