A process for the preparation of 3-phenyl/heteroaryl-6-phenoxy-8-alkylamino-imidazo[1,2-b]pyridazine derivatives and intermediates of this process. A crystalline form of N-cyclopropyl-4-{6-(2,3-difluor-4-methoxyphenoxy)-8-[(3,3,3-trifluorpropyl)amino]imidazo[1,2-b]pyridazin-3-yl}-2-methylbenzamide. The compounds are inhibitors of the Mps-1 kinase (Monopolar Spindle 1 kinase; also known as Tyrosine Threonine Kinase, TTK).