Monazite is a light rare-earth element (LREE)-bearing accessory phase common in felsic granitic rocks, and strongly influences LREE concentrations in granites and the chemistry of melts and residues formed during partial melting. Cheralite-rich (high-Th) monazite-(Ce) has been recorded as rims on partially dissolved cores in a suite of granulite-facies migmatites generated by disequilibrium melting. High-Th monazite has previously been recorded only in granitic-pegmatite occurrences. Subidiomorphic monazite-(Ce) from leucosome, melanosome and mesosome consists of complexly zoned cores (up to 300 µm in diameter) containing 5.17–9.87 wt.% ThO₂, overgrown by essentially unzoned rims (containing up to 21.4 wt.% ThO₂). Uranium contents are average for Th-rich monazite-(Ce) (0.22–3.17 wt.% UO₂). Th enrichment (relative to LREE) in monazite-(Ce) rims is ascribed to the presence of fluorine-bearing melts (formed during the incongruent breakdown of biotite to produce a water-undersaturated melt), allowing the formation of REE-fluoride complexes in the melt, coupled with the increased charge balanced substitutions Th⁴⁺ + Si⁴⁺ ⇌ REE³⁺ + P⁵⁺ and Th⁴⁺ + Ca²⁺ ⇌ 2REE³⁺ into monazite-(Ce). Fractionation of Th and U (reflected by an increased in Th/U in rims relative to cores) may have occurred due to the removal by a CO₂-rich fluid phase in the melt. These interpretations are consistent with elevated CO₂ and F contents of granitic liquids produced during the water-undersaturated breakdown of biotite under granulite-facies conditions. Evidence for restricted monazite-(Ce)-melt equilibration and rapid melt removal is provided by the ubiquitous presence of partially embayed cores and unzoned rims.