British Actor William Rush, Known for 'Waterloo Road,' Dead at 31

William Rush, a British actor best known for the popular UK-based series "Waterloo Road," has died.

The tragic news was confirmed by William's mom, Debbie Rush, on IG Wednesday ... writing, "As a family, our hearts are completely broken, and there are no words that can truly capture the depth of our loss."

Debbie, who starred in the popular British soap "Coronation Street," also added that up until the very end, he was thinking about others as an organ donor.

William's cause of death hasn't been revealed.

He was best known for playing Josh Stevenson in the high-school drama "Waterloo Road" from 2009 to 2013 -- and even appeared in other big British hits like "Grange Hill," the original UK version of "Shameless," "Casualty" and "Vera."

He was 31.