United Kingdom, May 20 -- Sarah Michelle Gellar is always "there emotionally" for Alyson Hannigan.

The 48-year-old actress starred alongside Alyson, 51, on 'Buffy the Vampire Slayer', the supernatural drama series, between 1997 and 2003, and Sarah has explained how their friendship has survived more than 30 years.

The actress - who has Charlotte, 15, and Rocky, 12, with husband Freddie Prinze Jr - told Us Weekly: "Moms understand that friendship doesn't mean I have to call you every single day.

"There's never a crisis time in my life that there isn't a text from Alyson. I don't mean that in a bad way. That's how you maintain a friendship: by knowing the things that [matter].

"We don't miss birthdays. We don't miss the big ones. Those ...