The actor, who is most famous for playing comedy character Frasier, has been dating air stewardess Kayte Walsh, 29, since August.
Earlier this year he split from his third wife, former Playboy model Camille Donatacci, after she cited irreconcilable differences.
And now Kelsey’s representative has confirmed the star is looking forward to tying the knot once again.
“They are engaged. They never really announced it, they are very happy and very much in love,” Stan Rosenfield told RadarOnline.
Kayte was spotted wearing an engagement ring when the pair arrived at a Washington train station last weekend.
She suffered a miscarriage in the summer after they announced she was pregnant with the 55-year-old’s child. At the time, the actor said he was struggling to find “solace”.
Kelsey already has two kids with Camille, eight-year-old Mason and Jude, who is six.
She has asked for primary custody of the children.