Last month, Bruce Jenner and estranged wife Kris Jenner filed for divorce 11 months after announcing that they were ending their 22-year-marriage. And now, Bruce has reportedly moved on from his relationship with Kris and is already dating Kris' longtime best friend Ronda Kamihira.

Sources close to the Jenner clan told TMZ that Kris, 58, is "extremely upset" that her estranged husband is hooking up with her pal, a 51-year-old divorced woman who has two children. "It really stings because Ronda never told Kris she started seeing Bruce," the tipster said.

"Kris is devastated," a source told People. "This was her former assistant and best friend of 20 years." The insider added that Kris "is just shocked" by the news. "She's so sad and completely heartbroken."

Kris and Ronda, who have been neighbors in Hidden Hills, Calif., are so close that they have even spent holidays at each other's residences. The two had also traveled abroad together, and their daughters have also become friends.

"Kendall and Kylie grew up with [Ronda's] two kids and have been their best friends," People's source added.

Bruce, 64, and Ronda first publicly stepped out in Los Angeles at an Elton John concert on Oct. 4. A source told Us Weekly that the rumored couple was joined by Bruce's son Brandon Jenner and his wife Leah for the outing, where they dined on chicken lettuce wraps and popcorn in Hyde Lounge at the Staples Center.

However, a source tells E! News that Bruce and Ronda are not dating.

"Ronda is one of Bruce's longtime best friends in the world," the insider explained. "They are definitely not dating. Trust me, anyone suggesting that is barking up the wrong tree."

During an episode of Beyond Candid With Giuliana, Kris told Giuliana Rancic that she absolutely sees herself having a romantic relationship with a new man in the future.

"I want to definitely be in love, I like being in love, I think there's no better feeling in the world. So yeah, I mean that would be amazing," Kris said.