How did Bertrand Russell first become connected with Alfred North Whitehead?

Alfred North Whitehead and Bertrand Russell first connected at Trinity College, Cambridge, where Whitehead served as one of Russell’s teachers. Whitehead first recognized Russell's brilliance while examining him for entrance scholarships in 1890, when Russell was a freshman studying mathematics. Over time, the two developed a close friendship that eventually led to their extensive professional collaboration on the foundational work of logic and mathematics, Principia Mathematica.1