The 41-year-old "Younger" actress said her obsession with him went too far , reported US magazine.
"I had such a crush on him. I journal and cut things out from magazines for inspiration, and I was going through old journals and out fluttered a photo of Milo.
"I wasn't a teenage girl. I was in my late twenties when this happened!," Foster said.
Ventimiglia, 38, joined the popular series in 2001 as Jess Mariano, who dated Rory Gilmore (Alexis Bledel).
Foster didn't film any scenes with the "Heroes" star for the upcoming Netflix reboot, but she did share the screen with ex-husband, fellow Broadway star Christian Borle.
"He's a wonderfully talented guy, and it just became an opportunity where we could do this together. The two of us are the stars of the Stars Hollow musical. It was amazing to share that experience with him, especially with our history," she said.
The release date for "Gilmore Girls: A Year In The Life," is not revealed yet.