Bobbi Kristina can't get enough of "adopted" brother Nick Gordon. Last week, the wild child of the late Whitney Houston took the obvious next step in her somewhat incestuous relationship with 22-year-old Nick -- they got matching tattoos. Ironically enough, the tattoo the lovers now share is the initials of the woman they both considered to be their mom. How many lovers can boast that one? Houston took in Gordon as her adopted son when he was 12, and Bobbi Kristina and Nick lived like siblings for more than 10 years. To commemorate what would have been the "I Will Always Love You" singer's 49th birthday, Bobbi Kristina and Nick got the letters WH surrounded by doves tattooed on their wrists. But the festivities apparently didn't end there this week. Bobbi Kristina posted a photo of her and Nick kissing tenderly on Twitter. She also happened to be sporting a giant rock on one certain finger. She captioned the picture, "1 of the main reasons why i even smile today.:) iloveyoubooboo, forever&always. "it's just US now"...@Nickdgordon {<3}" No word on whether or not an engagement was also part of their gift to the late Houston. All of these eye-opening events are certain to be available for public consumption when Houston's reality show The Houston Family Chronicles debuts on Lifetime next month.