Sean "Diddy" Combs broke his silence Sunday about the death of his ex-girlfriend last week.

Kim Porter, 47, was found dead Thursday at her Los Angeles home.

PHOTO: Kim Porter attends the premiere screening of Amazon Original Special 'An American Girl Story - Melody 1963: Love Has To Win,' Oct. 10, 2016, in Los Angeles.
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Kim Porter attends the premiere screening of Amazon Original Special 'An American Girl Story - Melody 1963: Love Has To Win,' Oct. 10, 2016, in Los Angeles.

The cause of death has not been determined.

(MORE: Kim Porter dies at 47)

"I've been trying to wake up out of this nightmare," he posted on Instagram. "But I haven't."

Porter was the mother of Diddy's three children: their son, Christian, 20, and twin daughters, D'Lila Star and Jesse James, who are 11 years old.

PHOTO: Kim Porter and Sean "Diddy" Combs arrive at "The Rock N Roll of Hip Hop" party," June 26, 2009, in Beverly Hills, Calif.
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Kim Porter and Sean "Diddy" Combs arrive at "The Rock N Roll of Hip Hop" party," June 26, 2009, in Beverly Hills, Calif.

She was an actress who appeared on the TV series "Wicked Wicked Games" and the film "Mama I Want to Sing."

PHOTO: Sean Combs arrives for the 2018 Met Gala, May 7, 2018, at the Metropolitan Museum of Art in New York.
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Sean Combs arrives for the 2018 Met Gala, May 7, 2018, at the Metropolitan Museum of Art in New York.

Diddy had an on-again-off-again relationship with Porter.

"I don't know what I'm going to do without you baby," Diddy wrote Sunday. "I miss you so much."

PHOTO: Sean Diddy Combs poses with his girlfriend, model Kim Porter and their children as Combs receives a star on the Hollywood Walk of Fame in Hollywood, Calif., April 25, 2008.
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Sean Diddy Combs poses with his girlfriend, model Kim Porter and their children as Combs receives a star on the Hollywood Walk of Fame in Hollywood, Calif., April 25, 2008.

The two split shortly after their daughters were born.

"Today I’m going to pay tribute to you, I’m going to try and find the words to explain our unexplainable relationship," he added. "We were more than best friends, we were more than soulmates."