GO:0007181

The aggregation, arrangement and bonding together of a ligand-bound type II transforming growth factor beta (TGF-beta) receptor dimer with a type I TGF-beta receptor dimer, following ligand binding, to form a heterotetrameric TGF-beta receptor complex. [GOC:jl, Reactome:REACT_7425, Wikipedia:TGF_beta_signaling_pathway]