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"Kayte and I are marrying because we are engaged, and we are engaged because we are in love and see no reason to postpone our happiness any longer," Grammer, 55, told People.com.
The "Fraiser" star's soon-to-be ex Camille, 47, filed for divorce over the summer, ending the pair's 13-year marriage to Camille. They have two children together.
With the ink still drying on his divorce papers, Grammer told People he saw no need to wait to get hitched again.
"We are planning something we wish to be a private affair among several of our friends. Anything else is conjecture and false," he told People. "Kayte and I are the only reliable source for this story. End of story."
Walsh was pregnant with Grammer's child but has a miscarriage this fall.