Loud engine knocking - big end?

[NotAnotherHill]

Had to abort my ride today. The bike developed a loud knocking sound coming from the bottom end of the engine. When I stopped and revved it in neutral, no knocking. But when riding the knocking is regular and increase with speed. I can also feel the knocking. I'm not at all mechanically savvy, but have a feeling this might be terminal. Any advice?