According to the US publication's report, Reese declared war on the Ellen Degeneres Show host after launching her own talk show, Shine On with Reese, a nine-part series featuring interviews with A-list celebrities.
"Right now, Shine On doesn't have anywhere near the reach of Ellen's talk show," an insider told GLOBE, "But Reese has much bigger plans. She wants to get absolutely tip-top A-listers like her friend Jennifer Aniston."
Reese's scheme to taken Ellen's throne includes plans to have celebrities do her show exclusively, tying them up so they can't appear on Ellen.
"Reese is ruthless," dishes the source. "She wants to make a big splash and she's ready to get down and dirty to do it."
However, according to GLOBE, Ellen is "not having it."
"Ellen wants to fight fire with fire," an insider spilled.
The two's heated rivalry goes "way back" a source also tells.
"Reese and Ellen have always been competitive. They constantly like to one-up each other."