The model died on Thursday at the age of 47, and a source tells ET that the rapper is still in "complete shock" over the tragic news.
Diddy and Porter were "very close," the source says, after dating on and off for 13 years. They also share three children together, twin daughters Jessie James and D'Lila, 11, and son Christian, 20.
"They went through some tough times but truly came out on top," the source says. "Sean constantly raved about what an amazing mother she was to their children."
"Sean is truly devastated and is desperately trying to come to terms with how he will move forward without Kim," the source adds. "He is truly in shock. Their closest friends are being the best support they can be at this moment and surrounding him with love."
In addition to Jessie, D'Lila and Christian, Porter also has a 27-year-old son, Quincy, from her former marriage to Al B. Sure!
"This has been a complete shock to all of Kim's family and friends," the source shares. "In the weeks prior, she seemed happy and had recently been traveling. Two weeks before her passing she really seemed herself, hanging out with friends, going out to dinner and in good spirits."
"Kim was truly gorgeous both inside and out," adds the source. "She was such an incredibly good mother, so present, and so loving. She was almost inseparable with the twins."
As previously reported, a Los Angeles Public Information Officer confirmed to ET that North Hollywood police officers responded to a death investigation call at a Toluca Lake, California, residence on Thursday. Additionally, a spokesperson for LAPD told ET that no foul play was suspected at the time, adding that the cause of death is still undetermined pending a coroner investigation.
"Sadly, I can confirm the passing of Kim Porter," the model's rep said in a statement. "I ask that you give the families privacy at this time."
Diddy always spoke highly of Porter over the years, including in interviews with ET. When we spoke with the rapper in 2006, he even said he hoped they would be buried "side by side" one day. Watch below: