A three-parameter family B = B(a, b, c) of weighted Hankel matrices is introduced with the entriessupposing a, b, c are positive and a < b + c, b < a + c, c ≤ a + b. The famous Hilbert matrix is included as a particular case. The direct sum B(a, b, c) ⊕ B(a + 1, b + 1, c) is shown to commute with a discrete analog of the dilatation operator. It follows that there exists a three-parameter family of real symmetric Jacobi matrices, T (a, b, c), commuting with B(a, b, c). The orthogonal polynomials associated with T (a, b, c) turn out to be the continuous dual Hahn polynomials. Consequently, a unitary mapping U diagonalizing T (a, b, c) can be constructed explicitly. At the same time, U diagonalizes B(a, b, c) and the spectrum of this matrix operator is shown to be purely absolutely continuous and filling the interval [0, M (a, b, c)] where M (a, b, c) is known explicitly.If the assumption c ≤ a + b is relaxed while the remaining inequalities on a, b, c are all supposed to be valid, the spectrum contains also a finite discrete part lying above the threshold M (a, b, c). Again, all eigenvalues and eigenvectors are described explicitly.