Let $P$ and $Q$ be positive definite matrices. Consider the following matrix equation $$\label{star}\tag{$\star$} XPX^\top - P = -Q, \quad X\in\mathbb{R}^{n\times n}. $$ Moreover, given a matrix $M\in\mathbb{R}^{n\times n}$ let $\sigma(M)$ denote the spectrum of $M$ and $\lambda_{\min}(M):=\min_{\lambda\in\sigma(M)} |\lambda| $, $\lambda_{\max}(M):=\max_{\lambda\in\sigma(M)} |\lambda|$. > **My question.** Is it true that any solution of \eqref{star} can be written as $X=(P-Q)^{1/2}TP^{-1/2}$ with $T$ being an arbitrary orthogonal matrix?