Pita: At Ratha-yatra, Srila Prabhupada told us the story of how Krishna took the form of Jagannatha. He said, “One day Krishna was walking through the halls in His palace in Dwaraka when He heard Rohini and Rukmini talking. Rukmini said to Rohini, ‘Last night when He was sleeping, I heard Krishna saying the name Radha, Radha, Radha. Who is Radha?’ Rohini said, ‘Radha is very special and the relationship between Radha and Krishna is very special. Let me tell you the story of Radha-Krishna’s relationship.’ Krishna listened while Rohini told the story and as He listened He became stunned and He took the form of Jagannatha with big eyes and a big smile.” Prabhupada smiled broadly, “Later Subhadra came by, saw Krishna stunned, also listened, became stunned and took the form of Subhadra as we see in the Deities. And the same thing happened to Baladev.“
Reference: Memories Anecdotes of a Modern Day Saint – Volume 3 by Siddhanta Dasa