An Erika Jayne t-shirt seen on "Mad Men" actress, January Jones, is making fans crazy. "The Real Housewives of Beverly Hills" star posted an image on her Instagram account of January's photo that she put on her own page. January, who played Betty Draper on the hit AMC show, is evidently a fan of Erika's.

'Mad Men' actress dons 'RHOBH's star's fan t-shirt

The t-shirt that January is wearing is of Erika's famous song, "XXpen$ive." It shows a provocative illustration of Erika posing in front of a white car in Beverly Hills. Erika was seen last season performing in concert and making the video for it.

Some of the actress' fans also love Erika Jayne, with one commenting that the "RHOBH" cast member is the "21st century Betty." Others wrote that they want an Erika Jayne shirt, too, and are clamoring to know where they can get one. Fans on both Instagram pages want to know where they can purchase the t-shirt. A simple online search will have many options of where to purchase the shirt. The image that January has on was shows the lettering backwards, however. It's hard to tell, but she must have been standing before a mirror to get the shot.

Celebs dig Erika

Who knew that January Jones was a fan of Erika Jayne? There are other celebrities who are fans of Erika's. In season 7 of the show, Dorit Kemsley's husband, Paul Kemsley, told Erika that Boy George liked her work.

It made Erika's day to hear that a major pop icon was even aware of who she was. Since Erika has joined "rhobh," her star has shined even brighter in the music and entertainment industry. Fans got a chance to learn more about her glam squad and behind-the-scenes life on the show, which has given her more worldwide fame.

"RHOBH" has also opened many doors for Erika Jayne in the two seasons that she's been a full-time cast member on the show.

She was in the spring 2017 season of "Dancing with the Stars" and has made several appearances on "The Young and the Restless." Former "Real Housewives" cast member, Eileen Davidson, gifted Erika with a script to be on the show for her 45th birthday celebration.

What do you think if January Jones wearing a t-shirt showing that she's a fan of Erika Jayne?

It hardly seems like the kind of thing Betty Draper would've dared to wear, but January is far more carefree than the reserved and uppity housewife of a successful advertising executive.

"The Real Housewives of Beverly Hills" season 8 will premiere later this fall on Bravo.