Cook the fettuccine in a large pot of salted boiling water according to package instructions until al dente, about 8-10 minutes. Reserve 1/2 cup of pasta water, then drain.

In a skillet, melt 2 tablespoons of butter over medium heat. Add the lobster meat and crab, sauté for 2-3 minutes until heated. Remove and set aside.

In the same skillet, melt another 2 tablespoons of butter over medium-low heat. Sauté the minced garlic for 30 seconds until fragrant. Pour in the heavy cream and simmer for 3-4 minutes. Stir in Cajun seasoning.

Reduce to low heat, add grated Parmesan cheese, stirring until melted. Mix in the lobster, crab, and fettuccine, ensuring everything is coated.

Gradually add reserved pasta water to adjust the sauce consistency, mixing until achieved.

Remove from heat, garnish with parsley and serve immediately.