Sarah Michelle Gellar celebrates Freddie Prinze Jr.'s 50th birthday

Sarah Michelle Gellar has paid tribute to her husband Freddie Prinze Jr. on his "milestone" 50th birthday.

The Scooby-Doo actor celebrated his special day on Sunday, with his wife taking to social media to mark the occasion.

Sarah Michelle posted photos of the pair posing together, including one shot of the happy couple pulling silly faces and another where the actress planted a kiss on smiling Freddie's cheek.

In the accompanying caption, Sarah Michelle wrote on Instagram, "Happy Milestone Bday @realfreddieprinze."

She continued the birthday tribute by praising their long-standing marriage, as she added, "Age is simply the number of years the world has gotten to enjoy you. And no one has enjoyed you more than me."

The Buffy the Vampire Slayer star wasn't the only famous face to mark the special birthday.

A series of celebrity friends including Amanda Kloots, Lisa Rinna and Heather Dubrow also sent their best wishes as Freddie turned 50 over the weekend.

Freddie and Sarah Michelle have been married since 2002 and raise two children together, 16-year-old daughter Charlotte and 13-year-old son Rocky.

The 48-year-old actress was recently quizzed on the secret to a happy, healthy relationship.

When asked by E! News to divulge the one rule that has kept her marriage on track for more than two decades, Sarah Michelle replied earlier this year, "Separate bathrooms. That's what I always say."